I ended up sectioning in an AMD rear frame rail into the front of the original rail (anyone need the front part of a rear rail?). The dimensions matched up great where the splice was done.

Differences I noticed were in the sharpness of the lower end of the frame rail where I made the splice. The AMD rail was a little sharper. I also needed to refold the rear crossmember flange of the rail as it made the turn a little "early". I would've had to mount the new rear spring hanger forward on the rail a bit to compensate and I preferred to refold the flange area. I've seen other rear rails extending further before going sideways for the rear crossmember, so this seems to vary a bit.