How do you fix this?

No need to return to stock, as the car is already far away from there with the 4 speed thrown in.

Looking at it, I'm thinking along the same line. Drop the old cross member, weld in some plates to the floor support and then install a new cross member.

Right now, I'm worried about what else I don't know I don't know. lol

My local mopar club has been pretty helpful. I'm hoping one of the guys in it can assist me. I'm a pretty decent shade tree mechanic, but don't even own a welder.