the 53+ units utilize a side mounted engine pump vs the N belly pump.. but actual test procedures are similar.
you could put a gauge in the port on the head of the engin emounted pump, or in the plug spot on the 3x5 option cover on the hyd top cover.. or if you have a remote, adapt it the gauge to a qd and use that.
on the remote.. just deadhead the rmeote with the gauge in for a moment.
on the other 2, you have to chain the 3pt arms down and then exercise the lift.
I'd use a liquid filled 0-3000 psi gauge.
On the old N it was 1500-1700 psi. i don't have my manual in front of me for the pressure on an 00 series. can't say if it's 1700, 2250 or 2500. 2500 is a common ag hyd pressure.
When i get to my manual I'll update the thread.
in the mean time, you really should get at least an FO-20 service manual and a master parts catalog.
soundguy