Need advice on frame connectors

4spd,
First of all please consider 1 1/2" x 3" and dont cut your floors, just weld to them. The 3" will slide right over the rear rail and be very strong. I agree that you need your car square to the ground, but when the factory makes up the frame there is no drive train in the car.
Check out my thread on the frame connectors I put in.
Andrew