Driveshaft Dilemma!

By now I feel like a candidate for the Darwin Award! Let me begin: about a year ago I decided not to change my Black 66 Barracuda from an automatic to the 833 4spd that came in the van I bought for the 318 4bbl engine - it was a B-Body trans. I bought a 904 out of a 75 Valiant 318 car along with the drive shaft. The guy who sold it to me said it would need shortened by 2" because they increased the wheel base in the 70's. I compared it to the shaft from my green 66 car and indeed it was 2"s longer. Off to the machine shop. We put the engine and trans in and tried the shaft - still too long. I got a chart someone had posted on this site with the proper lengths for a 904 with 8-3/4 rearend. Back to the machine shop. Today I went to install it again and realized the seat on the yoke for the bearing caps of the U-joint measures 3-1/2" and my U-joint is only 3" across. Can you spell SLOP - at least a 1/4 inch. Any suggestions or does anyone along I-80 between Pittsburgh and Chicago have a 904/8-3/4 rear driveshaft? I will be taking a load to East Chicago either Tues. or Weds.