Pinion angle relative to frame?

What you want is the transmission/ crank centerline -- and the pinion parallel under full throttle.

I realize that with different springs this works out, well, "different"

An accepted starting place is 2.5* down from crank centerline. THIS IS NOT (necessarily) the same as the body "level." (Look at a typical intake manifold---the carb is not "tilted forward," the rest of the manifold is, rather, "tilted back.")