Matt,
It is easy to install your IP incorrectly, the timing is very different for your version than for newer pumps. I would say it is worth a look if all else is sorted out first. On your pump, engine should be at 20 ATDC for firing sequence on #1 cylinder, then turn the pump until the timing marks on the collar and spline line up exactly, then fit it back together. As I recall it is 20 degrees different from the newer pumps.
Best,
g
'64 230sl, fully sorted out...ooops, spoke too soon