I recommend a bms/monitor. $250.
However, these require re-configuring. Not technically difficult, but very labor intensive.
I would need $3k for wired kit. Same as what Grant posted in his Spark thread.
He shows step by step mounting.
16s modules need to be electrically divided into 8s + 8s.
I can show you exactly how to do it. @Mr.Vern mentioned tapping the cells. This is similar to that. I may have posted the process previously.
Hereās Grantās thread.
Before you go any further you should answer the question; what are you trying to accomplish?
Replace current worn out batteries with something that is low/no maintenance and will last forever
Improve range
Improve performance
find a fun hobby that will keep you learning and engaged
The answers to these questions will help you find the right solution.
My main goal is to improve range. I have the old T1 controller which over heats in the Summer when going up steep hills. Will the Li-ion change help this issue as well as increase range?
Only issues with older cars (1999-2004) is when you remove all that Flooded lead acid batteryās you remove 400 lbs of weight.
Yes your car gets lighter and then the stock shocks virtually āLOCK OUTā The car bounces down the road. So if your gonna do a Lithium conversion on a older car you need to find some softer more compliant shocks the front is a Must the rears are debatable.
So if you wanna tackle that issue you can move on to step #2 cost. David can sell you everything you need, thatās gonna set you back $3-5 k depending on what you go with, issue #3 you still have to do some work yourself. I imagine if all you want to do is drop in a kit and have it turn key and pay someone like David to Pre wire your BMS and make all your cables your gonna pay 7-9k for a complete turn key system.
@grantwest
He needs your stacked Bolt pack if it ever gets there. 12kwh and fits in the front.
Itās already wired for bms. All the work is done!
As usual Dave with the good Idea. Post a link to the guy that put a Split Bolt Pack innthe front of his 2000 Gem
If you want to improve range, the next question - how much range is enough range? I can go close to if not over 40 miles in the hills of my community with my dual Volt pack ~100Ah rating. Others get less range and Iām not sure why. Could be that I use the regen a lot coming down the hills. It certainly isnāt because I drive mellow 
A single set of Volt batteries is close to the range on the Leaf I believe (please verify) and should get you a solid 15 miles and likely more from what I have seen from others. Is that enough? You have enough room in your car to do 3 of those packs. I have 2 in mine and had planned on adding the third if needed, but I will never use all the range that I have now so Iām going to use the other packs in another car.
Concerning the question of voltage and heat. In theory, a motor can run cooler with higher voltage if it stays within the sweetspot of its design. For the sake of what you will be doing, I would anticipate more heat or the same. If for no other reason than you will be running much harder because its so fun. Some on here have put heatsinks on their controllers to cool them a little better. In the end, you will probably just have to take it easy when its hot and you need to climb 
The suspension issue that Grant mentioned is real but my experience has been a bit different than his. I have not tried it but am convinced that swapping a soft aluminum rod in place of the shocks would actually give you a better ride. My shocks on both of my cars do not compress at all. The aluminum bar would in theory be at least somewhat compliant. Not that Iām suggesting that as a solution. In my experience, the ride did not get any worse when I removed the weight. It sucked before and after! At first I left the lead batteries in the front as ballast out of fear that it would get worse. You can install 100Ah of batteries and still leave the lead in the front if it makes the ride more compliant. I have the air shocks but have decided not to install them til Fall because Iām enjoying the lake and golf course during the summer. Winter is project time. Iām sure it will make a huge difference in the ride though.
With the hills around here I would need more than 15 miles range simply because of the heavy use going up the hills. What would two packs run in cost? I have already made a heat sink for my controller and it works since I have not a 41 shutdown in a long time.
Now you have me drooling. Can I have that pack back?
Polaris says 95 miles.
75 easy in a legacy Gem.
The $2100 is for a double pack . Not ideal for an early model. 24s 130ah.
9kwh
Polaris says 70m
50 miles easy. Ask Grant. He has one. Heās my guinea pig. 
I donāt think I can talk Grant into this one.
60/70ah test prismatic
24 pcs for a gem.
Tested for capacity but not in a Gem.
I can replace any weak cell, or refund for all if you return them in 60 days.
Iāll include the bars with the first set for a Gem. These are >$100 batteries.
NOS
There is an early lifepo4 conversion on here 3yrs ago. Iāll look for it.
Inwo said you had a pack that would give me at least 50 miles. What would be the cost of that?
Grants 9kwh 50m pack is in a car he sold. His extra pack is 12kwh.
If you want NEW Lithium batteries that I have been providing for golf carts
for 7 years contact me at cruisin@live.com
Be advised: There are people selling 18S solutions as 72V replacements for stock lead batteries. This is dishonest and if you encounter one of them you should run. 18S is a 66.6V nominal battery and is not the equivalent of the 72V nominal your car came with. Your fully charged lead batteries should be closer to 80V at peak charge, 72V nominal.
There are folks on here and ebay who have been selling these solutions and countless victims have gotten on here asking for help because they donāt work. The seller refuses to refund their money and then sells them another pack with instructions on how to split it and make the car work. Be ye fair warned!
Stay on here and keep asking questions until you are sure you know what you are buying!
I agree with Mr Vern I have done 4+ Lithium gems now working in #5 & 6 right now. I would stick with the advice of people who have done it and know the pitfalls to avoid and what batteryās and acessories work. Nothing worse then spending money on stuff that is un tested and has no track record in a gem.
I just heard from a man in CA who sells new batteries and he told me that the people on the GEM forum were full of s*&^t. He had the personality of a crocodile. I am disappointed that someone hasnāt put together a package with what is need and covers all the variations in the installation. Iāve built two replica cars and restored several others so I can handle the labor but there is nothing I hate more than having to order on line and then wait another week for one part to arrive. Only to find out that it is not the right part. I e-mailed the guy in Arizona but he no longer deals with this stuff. The California guy said I should only use Cobalt batteries and no Chinese stuff. He also said a lot of the used batteries are from flooded cars and will fail in no time. What a way to get info huh?
Was the guy you were talking to was his name Alan ?
I have been playing with Gems for a while now. I havenāt found anyone with more Lithium gem conversions then the people here!