If you care, I have the original specs for this back hoe, as I have one myself. The original pump is listed as 8 gpm, @ 600 rpm, and 2000 psi. it was originally a Vickers 740687 which replaced the 735844. And yes, the Prince pump available from Northern Tool #1051 in their catalog, is a perfect fit for this unit. Just in case anyone else is having this sort of problem.
Have Fun, Stay Safe.