Nice build, Ive been planning to do same project. So far I discovered that the "key"to a hydraulic phd is the motor itself, the correct one to be more specific. Fortunately for you , you had the correct motor off your 2 man towable phd which is critical to a hphd for a CUT. Gpm, rpm,shaft size,torque/hp,psi, were already all to the correct specs for your build. Ive researched online mfgs of towable augers and they do give out the brand and model of the motors on their units.
I know your hphd motor is now encased, is there any ID of that mfg and model of your motor? Spending hundreds of dollars on a motor just to have one spec wrong would suck.