I bought mine as a kit from Keisler engineering, now owned by Silver Sport Transmissions. They made the driveshaft that fit for my engine, car and rear. I'd be willing to bet if you contact them and tell them what you have they will be able to build you the driveshaft you need, I'd also suspect they would tell you what length you would need if you wanted to make one locally. If it were me, and I couldn't find anyone who has done the same mod as you, I'd wait until the tranny and rear are in place, then measure and have one built. That way you will get exactly what you need.

I forget what the u-joints were when I got mine, but as the joints are smaller in the Chebby 8.2 than the BOP 8.2 I had to get a hybrid joint, with two large bearings and two smaller ones. I didn't realize my bird had a chebby rear in it when I ordered the kit. Duh!