I think the most important thing that will help you answer a lot of your own questions is to measure absolutely everything. You'll want to have your engine set back to the right point so that it doesn't interfere with the firewall, and you'll want your front suspension set so that the wheels are centered in the wheel wells (stock location, I assume).

There is no real specific angle requirement for a SBC, although the closest to level you can get is always best. If your engine is angled enough to not get even fuel distribution then something is majorly wrong. You should be more concerned with the oil pump pickup location in the oil pan, in my opinion.

Another thing to realize is that if you're trying to set all this with no body on the frame and without your final wheel and tire sizes, that things will change once all that is done, and you need to figure that into your setup. Make sure you measure a SBC and know where it needs to go (and mark it out) before you set up your front suspension so that everything goes smoothly. The driveshaft angles are the least of your concern at this point, as they can be dealt with when you set the motor in, and it can be set where it needs to be.

1946 GMC Pickup - S-10 Frame, 455 Buick, TH400, original patina.

My 46 GMC on Photobucket