While this thread is being dug up from the grave...here is some relevant info from my truck arm build on my 62 nova. Its still not quite done, my rear axle is being shipped to me, but once that arrives I can finish it off:
My floors were rusty, so I cut them out to get this project underway:
Here is my rear suspension donor, i got this whole piece and a 12bolt truck rear end for $100 CDN.
Here is the truck arm crossmember getting cut in half so it fit:
The crossmember with cut down mounts now welded on instead of riveted:
Mock up of the crossmember and subframe connectors, I've decided to go with 2x3 tube(its 2x2 in the pic) for the crossmember tube so I can drop it an inch lower and still have the 2x2 subframe connectors line up. Still to do is build a tub bridge over the driveshaft to tie the two sides together: