[dsraven]

I guess one way to know if the axle is set up to have an offset pinion would be to remove the brake drum or disc on both sides, clamp a length of angle iron onto those flanges to act as a straight edge that will extend the plane of the wheel mounting surface. do that on both sides and lay the angle iron on some jack stands so they will be at the same height as the pinion. then simply use a tape measure from the angle iron to the pinion on each side and compare the results. thats what I do and it works. thats how i come up with a real axle track width dimension on different donor axles at a wrecker or whatever.
really, if the pinion is offset and the engine and trans are also offset by roughly the same amount and the engine/trans are parallel to the frame, and the rear axle is perpendicular to the frame, then it should work out fine. but, if the pinion is offset and the engine trans are not then that is not a big deal as long as the axle is perpendicular to the engine and trans centreline. u joints can work that way. the frame is just what holds all the parts together.