42RH / A-500 in a Duster with pictures.

If the engine is set where it was angled at from the factory, then go with it. The more critical angle is on the rear axle itself. That's where the most degree of movement is going to come from and will be exerted on the rear u joint anyways. If you havent messed with the rear axle pinion angle, I would say wherever the trans is at with the engine at its stock angle is fine.

Since I have no drivetrain in the 69. I will mock it up the way I mentioned in my last post.