Frame Question

[Tazfink]

I have a '66 C-10 Fleetside Long Box. My trailing arms are HASHED!!!! Rusted through and splitting apart. So, 2 years ago I purchased a '72 Chevy C-20 frame that was equipped with trailing arms. The truck was supposedly from Arizona so the trailing arms and the frame are very solid. I pulled the trailing arms off to replace the ones on my '66.

Here is my dilemma, my '66 frame is getting pretty rusty right above the coil spring mounts and it may be slightly tweaked. The story goes that my aunt had hit a rock out in the field/pasture hard enough to dent the transmission crossmember (I assume this is why my engine mount holes never line up).

What are the differences between a 66 and 72 frames?
What are the differences between a 3/4 and 1/2 ton frame?

I have the frame drawings of the 66 frame but not for the 72. Anyone know where to find them?

Just to throw another variable into the equation I have access to a '74 C-10 Fleet Long Box. I was thinking of pulling the front crossmember/suspension off of that and putting that on to get disc brakes.

Any insight would be greatly appreciated!!