I would set the motor in place and try to get it as level as possible and centered with the rearend. Any radical angles can create vibrations due to the pinion angle with the rearend. Once the motor is in place, verfiy "all" your clearances with the steering, fan/radiator, firewall, floor, exhaust, etc before bolting/welding it into it's final place. The more you modify (steering, rearends, etc) the more it makes sense to tack things in place and think through how each component will work in relation to the others. The best bet is to look at similar configurations with the same motor and transmission, etc and look for potential gotchas.
Hope this helps a little...
-Rich
