Thanks, Catman, for the reply. Today, I got enough fittings to do the FEL circuit-to-post driver contingent on what I found out today on this site. When I got home, I disconnected one of the FEL curl circuits and applied pressure to the joystick for that circuit and could tell that the hydraulic system was under load. I didn't expect that -- I figured that with the circuit dead-ended, it wouldn't do that so next, I disconnected both of the curl circuits -- same thing on load. Maybe it would have behaved differently if the circuit had been completed to the post driver which is itself an open center circuit?
So after that very fast experiment, I figured that I should probably just get the Power Beyond kit and be done with it. However, after looking at the diagram again closer (see attachment), it appears that the power beyond for the 4000 series is mounted directly above the hydraulic fill which is needed for the fluid dump for the post driver. Any confirmation from someone that has a 4000 series CUT?
So, that's where I am right now. Again, help is appreciated!