It is good you are researching instead of just doing, you would have been greatly disappointed the way this would have turned out for you. Yes, this has been considered quite a few times by others. Yes, hopefully you did try a search first, as that is where I obtained this a while back. This info was not as easy to find as others, but it is there. The numbers you are in search of are 25gpm at approximately 1800rpm engine speed (max recommended), with a 1750psi relief valve which is integral to the directional control valve. I think it is cheaper and easier to buy a 925 to begin with if that is what you want (I did), but each their own.
An electric pump will not even come close to this. If you don't want to do a trans mounted PTO unit for whatever reason, I'd suggest you next investigate a belt driven clutched unit. Forgot the flow rates on those, but they are available in at least several different volumes, and at least half the rating of the PTO one, or more. They are not low cost though either. You could probably build one cheaper with a small used Honda GX gas engine and a hydraulic pump from Northern, all mounted atop of your pass side tool box (if 923).
