I didnt read much so forgive me if I missed anything.
You SERIOUSLY need to address your rear subfloor if you havent already. Having a 328 doesnt help you at all, track car or grocery getter your subfloor will tear , guaranteed.
Before you spend a penny on appearance crap , make sure you replace your subframe carrier mounts, all 3 diff bushes, center support bearing, guibo , rtab and your engine and tranny mounts.
If your subfloor already has a crack , best way to go about it would be to scrap the car and buy a 02+ car .Or you can try repairing it endlessly
I recommend you NOT buy anything for your car untill you check your rear subfloor