Can't get Pro Parts headers to fit.

My experience with Schumacher mounts, albeit to a small block K, was this to get my engine centered was this;

Put engine in with trans originally, could not get it centered to save my life. Tried shims that came with my schumacher tri y's, no go. It was not off much, so I felt leave it for break in and fix after.

Had to pull engine for a noise, fixed it and reinstalled. Just pulled and reinstalled the engine only, trans stayed this time.

My engine went in perfectly centered as I lowered down about 1.5 inches away from the trans, made sure trans was jacked up perfect and straight, made sure engine was level, then pushed engine from the front and it slammed into the trans perfect and is 100% level now.

Probably a useless post from a newbie, but I found that the biscuits sideways act like sliders without the trans dragging it at the end and allowed for lots of alignment before final mating of the two.