OK Bob that is the Ossillating pump and mounting to the back plate is the best place to do it if the inlet and outlet are to the sides in otherwords perpendicular to the crankshaft or in the plain of rotation.

The problem is, if this set up is used then its unlikely that the pump has been wetted out in storage and no doubt about it the ball will be stuck and this does cause many problems. It can be dissassembled and cleaned.

However this pump has no form of regulation like the regulating pump does and this makes using it on an inverted setup a bad idea in the first place. I agree with you the very first thing I would do is bypass the pump and try the engine agine.

John