It can't be done any better than Keith Seymore showed in his posts as far as this goes.
The only real reason the transmission angles down at all is to clear low floor boards.
On AD and TF trucks the stock centerline of the crank and mainshaft in the transmission sit pretty level. On sixes the carb sits level to the head and block. Get into the V8's and they started putting the engine and trans at a slight angle to clear the floorboards in cars and they made the intake manifolds so that the carb sits level . Now we install our engines at an angle to put the carb mounting surface level and that is why all too many guys think you have to set the engine up at an angle for U joints or drive shaft.
Transmission shaft and pinion shaft = parallel is the main concern. Don't listen to the ricky racers down at the spit and whittle club who say you have to have the pinion pointing down at an angle to compensate for torque, They were the ones who were always breaking U joints at the starting line at the drag strip with that nonsense but they are still around giving bad advice.
