Every battery/car is a one off and a little different. You may need help if not comfortable with 72v wiring.
To start, find a place to put the battery @BigT just finish his and can give you some tips.
Iirc, he removed the rear spat and slid the battery in on a plywood base.
After battery is in place connect your original battery cables to the plus terminal of battery and the black (neg) wire of bms.
I can then give you instructions to jumpstart bms.