The proper driveshaft for the Z V8 swap uses Chevrolet U-joints at both ends. If you use the Datsun U-joints, they can fail under hard use. Stealth Conversions has three different driveshaft flanges that bolt to the Datsun differential and use a Chevrolet U-joint (Dana-Spacer #1310).
1970–1978 Z cars (with the exception of 1975) differentials use the flange on the left. This is available as part #DAT-110.
1975 Z cars use the 2.0" pilot, and some 1979-1983 differentials (used in 280ZX cars) use the center flange. This uses 10 mm bolts, compared to 8 mm bolts, to attach the flange to the differential. This is available as part #DAT-110.2
300ZX cars often use the flange on the right. This is available as part #DAT-110-300ZX
Use socket head bolts (8 mm x 30 mm long, or 10 mm x 30 mm long) because it is difficult to get a box wrench around standard hex-head bolts. Use self-locking nuts to fasten the flange to the differential. Standard nuts have been known to come loose, with disastrous results. We recommend that you use Locktite® in addition to the self-locking nuts. If you get a driveline vibration in the car, always check the bolts on the differential flange to see that they are tight. If you still have a driveline vibration, check the front differential mount (or isolator). Replacing the front differential mount has solved vibration problems in a number of cars.