A TH350 shaft should fit. The 396 engine in my '67 short bed ate the TH700R4 that was in there before I bought the truck, so I swapped in a rebuilt TH350 I had it laying around. I used the same driveshaft with no modifications at all. Only had to move the trans cross member, drill some new holes, replace the TV cable with a detent cable and rebend the coolant lines, and away she went. I would love to have an OD in there, but I will have to have one made a little more robust to live behind the 396. That, and the cost was right for the TH350.
