Changing rear end angle.

[geezer#99]

You're going about it bassackwards!
With your motor in the frame sitting on the front suspension with wheels/tires installed, set your carb level and then install your tranny mount. Leave the rearend alone until you have the rest of the weight on the truck. Then set your pinion angle and install your driveshaft. At that point in time you'll know whether you need a one or two piece driveshaft to clear your truck arm mount. Otherwise you're spending a lot of time mocking up what you might need to change later.
JMHO