Any tips on fitting the US Car Tool Sub Frame connectors?

I did mine on the rotisserie. I knew the shell was square & straight and I didn't have to deal with overhead welding. I remember something funky about the fit, but I also didn't care for the way they ran across the floor. The rear frame rails are farther apart than the front and they're designed to connect at those points. I didn't want mine welded in at an angle so I had to modify them to run parallel to the rocker.

Totally worth it. The shell is so solid, it won't sit on jackstands when the floor is uneven-it won't contact the stand on a low part of the floor.