Pinion Angle/Tailshaft Bushing

All A/F-body A833s have identical dimensions, except for certain od boxes had the small output shafts. That would require upsizing the yoke to the 727 dimension

That cam likes to be reved.
Put a vacuum gauge on it and slowly rev the engine up to at least 3000. The vacuum will steadily increase. When it tops out, that is when the engine first becomes efficient.That is the minimum cruise rpm for best fuel economy. That can be considered the minimum engine speed.Reversion has stopped, and the air in the intake is now all moving in the same direction. The headers have finally stopped yanking fresh charge out into the exhaust system.This is where you start leaning it out to get some mpgs.And the oil starts to say thank you.
If this is 1800 rpm, then 1st will want to be buzzed up to 3300,and second to 3000.
>If it is 2000, then 2000/.54=3700 into 2nd, and 2000/.599=3340 into direct
If 2200, then 2200/.54=4074 into 2nd, and 2200/.599=3673 into direct.
Of course the engine will be happy to be shifted earlier,But then a smaller cam would be a great investment. It will make more torque down below the vacuum peak, possible even up to 3000/3500. More torque down there means more power. And less fuel useage. And cleaner,longer-lasting oil. And longer lasting cylinder walls.
If you are keeping the revs down, It seems to me that you and that combo are not so well-matched.I say this with no animosity, or criticism, only as gentle as I know how to.

Now that makes me curious, What was your thinking for installing the 3.91s?