i converted my PTO winch to hydraulic:
Hydraulic Conversion of PTO Winch.
i used about half of the A3 parts - hydraulic motor, shaft coupler, motor-winch mount, and reservoir.
if i had not found the A3 parts, i had planned to fab or source a motor-winch mount and have a local machine shop fab the shaft coupler to mate to an off-the-shelf motor. this would not be very hard to do. but, i found the A3 parts on here from a member for a good price.
in addition, you'll need a hydaulic pump and valve. the A3 uses an engine mounted pump and an air operated control valve. i didn't see the value in mimicing this setup and got a higher capacity PTO mounted pump and more standard motor spool valve.
you could likely use a power steering type pump. however, if you use a standard control valve, then the hydraulic system will be running all the time (the A3 control valve has a built-in bypass when not in use). another option is to add an electric clutch onto your engine mounted pump - this way you can disengage it when not needed (99.99% of the time).
there's a good bit of consideration to properly match a hydraulic pump and motor for a set of specific output performance criteria, but isn't that really that hard.
i like my winch much better now - a true one-man operation.
let me know if i can help.