I debated posting an "after action" but I thought maybe a Thank You was in order and another newcomer might benefit from my process. So, Thank you all for your help!
My tractor hydraulics now work perfectly.
My experiences: The FO-20 manual is your best friend. The much thicker Ford Service manual was less so because it assumes you have the official Ford tools. The FO-20 (as previously mentioned here) has work-around processes with common tools.
There are several youtube videos regarding NAA hydraulics and adjustments. Watch them once by all means then avoid as the adjustment process measurements are DIFFERENT.
I made a NCA502(hundred series) adjustment gauge from 1/2" square stock and a grinder in a few minutes. You need a digital caliper.
My piston and cylinder were fine. Air removed the piston easily. The hydraulic control valve came out easily, was cleaned and put back. The unloader valve gave me fits. I finally ended up pounding it out, sure I was destroying it & its bushings. All seemed fine and its back now with a new O-ring and cleaned up. On mine the cap with the internal threads started to pull the threads with my home made puller (bolt).
Parts- didn't need many. I ended up with two aftermarket gasket & o-ring kits from two different suppliers. Both were Tisco with same part number. NEITHER included the 0-rings fitting the tractor housing to top cover pressure and return lines (two). NEITHER included the baffle plate gasket on one end of the valve block. I had a cheap o-ring kit I ordered for the eventuality and it contained o-rings to fit the face seal.
I had researched the CNH (old Ford) on-line parts catalog and it gave duro values for the various o-rings so I had obtained a o-ring kit matching those.
I used a New Holland main cover gasket as it was a lot more substantial than the Tisco gaskets. I used a CNH cam follower pin. BTW my old pin was about 50% worn so, right on! I got the baffle plate gasket from CNH. I used a CNH felt ring and replaced the triangular plate with pin with a CNH part. Mine was rusted-deformed.
The sump was nasty (water mixed sludge) but cleaned up good. I found rust on the inside draft control spring, cleaned up good.
For the final adjustments- follow the guidance in FO-20 EXACTLY. You might need to read it ten times to get all the fine points correct (I needed to...).
Last thing (I think, sure I forget something), I used the CNH M2134D hydraulic/trans oil. They called it AMBRA 134G. It is some slippery stuff. The CNH parts counter guy tried to convice me to take some hytrans oil (whatever that is) so be careful.
Last word- don't underestimate the powers of condensation. This was done in zero temperatures in a barn in Maine. Every day the frost on the steel was impressive which after a little heating turned into lots of water. I guess I could have wiped up a 1/2 to a cupful a day off the project surfaces.