about 4 hrs to drop the pump R&R and put it back in.
I'd spend another 4 hrs and go thru the hyd cover as well.
many times a weak lift is a combo problem. worn pump, weak relief,a dn a very leaky piston cycl.
a leaky piston can cause a weak lift even if the pump is good as it maxes out at 1700 psi and 2.85 gpm with the engine screaming. if the leak is huge fromt he a bad hydro piston.. you won't get much lift.
you may or may not need a cyl.. I'd plan on a new piston, oring and backup washer.. top cover gasket.. 3 gaskets under the cyl.. pto flange gasket.. inspection cover gasket.. hyd pump lower gasket.. new relief valves.
if the pump chambers need repalcing you will need gaskets and parts for them.
have an fo-4 I&T manual on hand. you can fo this via cook book.
trhis is a good time to clean the rear sump singe the pto shaft comes out.
check it's seal as well.