Using that machinist's playdo for a tolerance checker, not sure what it's called, but I've used it in the past when re bearing rod & crank journals.. it'd make it easy to measure your cover atop your gears.. the closer you get to zero, the better & more reliable your pressure will be.
The inlet port on my Jung is like 8mm (?) vs 4mm on the pressure side.
Good work on the pump.. you'll be our cdn manufacture of scale hyds in no time!