Well, if I use the 10 HP motor, I would want the pulley sized so that I get more or less all 10HP out of the motor. (my pump is rated 5-10 HP).
It does not seem to hurt, so I will try. I will use the 10 HP reliance motor, first I will run it with phase converter just to verify the basics, and then I will buy run caps and will go from there, using 24 uF per HP. The motor may well start from these caps, actually. My phase converter's 10 HP idler starts from 194 uF every time.
At first I will use the pulley that would demand 7.5 HP out of this motor, which is a pulley that came with this compressor that matches the 10 HP motor's shaft as well, but if all goes well, I will try to up-size the pulley to get all 10 HP out of this system.
(the compressor had a 7.5 HP motor, I got the tank, pump and pulley but not the motor as part of the bargaining procedure).
Thanks a lot. I will hopefully get it to run today from RPC, proceeding from then on.