A MM will work with and dc gem motor, unless you get one with a “speed” magnet.
Yes, in kph reads 0-40 mph correctly.
Gem converter will work without issue at higher voltage input.
Spoof is a single wire connection to controller.
I recommend sticking with near stock voltage. Not a big deal to add cells later if you wish.
Voltage is only one parameter affecting speed.
Do you know the gear ratio of your truck. Mine is 12/1. Grant is 10/1. There is a, I believe, 14/1 also.
Some say stock motor can “grenade” at high speed.
I’m generally in mid 80v. 30-35 mph.
I will try to get the bms-24t and acc. together today.
For general information on the things I sell:
I mark things up, often 20-100%. 
That allows me to buy and test everything new that comes on the market.
It’s fine with me if you want to buy direct and save money. This is a hobby for me.
Still a couple $1k in the hole on Chargery products, after working with the engineer debugging and eating early product. Ask @grantwest about our early work.
Now that they work, everyone sells them.
I offer support and often repairs. And no waiting for delivery from China.
When I was in busness, my motto was.
“we service what they sell” 
I buy everything I can from David his support here is awesome. I’m not sure most Fourm members know you sell battery’s, chargers, BMS, spoofs, and a bunch of other stuff as well as repair it all.
It would be great if members knew your a one stop shop if the choose to.
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Shunt
Bms/lcd
DQ charge control
You’re thinking “that’s not right”! I’ll tell you what’s not right. Buying a new bms that’s not properly calibrated. 
Not only is #18 not low. It’s high! ???
Here is a second brand new bms, right out of the box.
This is my motor, bought it for 600 on eBay and the seller said he bought and never got around to installing it. How do I tell if it has a speed magnet?
It may be marked with a 2, 4, or 8.
If not, take the sensor off and hold one pole of a small magnet near it.
Stock 4 pulse magnet has 4 north and 4 south poles per revolution.
I’ve never tried, so I don’t know if it’s easily determined.
I am definitely in for a package deal with you, Dave. The most important part of that package is dealing with someone experienced and trustworthy.
I’ll get the inverter and solar boost charger independently but definitely appreciate the advice. Everything else that you already have in house, I will buy from you.
I know you like math!
On the ratio, again take the sensor off, so you can count motor turns through one revolution of (both) tires. 12=12/1 ratio.
You can do the same electrically. Meter (analog is best) from B- to green wire. About a 10v swing.
Move slow and steady 1/4 turn of tires counting pulses. 12 pulses = 12/1.
For more resolution roll one full turn and divide by 4.
Did you find Rodney’s calculator that I posted?
That calibration issue is a perfect example of why I’m glad to be working with you. I might not have noticed something like that until “Ka-Boom” 
Better to trust a trusty old multimeter.
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I’ll do some more investigating on the motor and gear ratio soon, and yes, I did get that calculator too. Thanks!
I did end up ordering an inverter like this one on eBay:
For the few other available 72 VDC options I looked at, I could find almost no information or reviews. This brand, “Reliable” seems to be a good quality option based on many reviews and videos of similar models.
There is a plethora of videos about their inverters and this one is a decent overview.
The eBay seller has been very responsive. He had me place the order on another listing (a little bit odd) with the correct price for my specifications that I messaged to him. It ended up at $305 because it was not US stock like some of their units and because I added a remote control option for $15.
Specifications (edited by me)
DC Voltage: 72 VDC
Voltage Range: 60-90 VDC
NO Load Current Draw: <0.6A
Efficiency: >90%
DC Connector: Cables With Clips or Car Adaptor
AC Voltage: 100/110/120VAC
Continuous Power: 2,500 W
Surge Power: 5,000 W
Waveform: Pure Sine Wave
Frequency: 60HZ
AC Regulation: 3%
Low Voltage Alarm: 64 VDC±1V
Low Voltage Shut Off: 62VDC±1V
Over Load: Shut Off Output
Over Voltage Shut Off: 91.2V
Over Thermal: Shut Off Output Automatically
Fuses: Short Circuit
Working Temperature: -10 to +50 Celsius (+14 to 122 Fahrenheit)
Working Humidity: 20%~90% RH non-condensing
Start: Soft Start
Cooling Ways: Cooling Fan
THD: <5%
Machine Size: 360 x 205 x 90 mm (14 x 8 x 3.5 in)
Net Weight: 5.18 kg (11.42 lbs)
I will update once I have it installed.
What size are the lugs on the Battery pack? The inverter has 3/8" lugs according to Amazon Q&A.
The ones that take a 10mm wrench. M8 I believe. Near to 1/4" .
I can build a drilled cu plate while you’re here if you remind me.
The B- is the shunt. 3/8" will work for that end.
I’ll be attaching the Gem Controller (appropriate size?), Inverter cables (thinking 2 or 4 guage?) and the input from the solar boost charger (probably 12 AWG). Other than a vice or hammer not sure how to put on cable lug connectors. I assume there is a special crimping tool. Just not something I have had to assemble before. I have made cables with Anderson connectors. I may be better off buying those from you Dave.
I can bolt a cu strap to to m8 battery post and drill it 3/8".
If you have a picture or drawing, will make something.
The bolt terminals are not design to support much mass. Heavy cables will need additional support.
Or you could run a light weight conductor to a distribution block.
If there are any electrical/mechanical things you might need, my brother’s store is next door. Allocate some time to shop. 7Rivers surplus.
I like the distribution block idea. 
Found this:
- Type: 1 Way In 5 Ways Out design power distributor, High-current multi-amp outputs
- Electrical Connection: 0GA/2GA/4GA X 1 Input, 2GA X 1+4GA X 2+8GA X 2 Output
- 2.8 x 1.3 x 1.8 inches
My 1-year-old makes better artwork than this, but you get the idea:
I could order a set… or you could 
Regarding the BMS, in some of the pictures it looks the screen and all wiring connections are one one box. Perhaps you are using a different version of the unit for testing but I just wanted to make sure that I would have the remote unit for on the dash and all the other wiring connections to the separate “brain” unit. I just wated to confirm. I did not even know there was an all-in-one-box unit. Thanks.