Starting point would be a '66 Valiant/Barracuda/wagon with a 904 and 8.75. If you can't find one, once you get everything mounted up, measure it up and have one made (which is probably the smart thing to do anyways). LOTS and LOTS of threads on here about measuring for a driveshaft, so I won't get into it here. Biggest issue is to not get too carried away with driveshaft diameter on an early A, the tunnels are tiny.
