I suggest a non traditional approach. Finish the boat into a clean useable condition and use it. It will never be Bristol but can be nice with a simple approach.
By simple I mean scrub all the interior with anit mold stuff then prim with alcohol based shellac based primer. NOT KILLS. The...
From your description the top controls seem the problem. Try disconnecting them from the bottom controls and see if they are still stiff. That would point to cables.
It's not necessary to go to the trouble of using a jack etc to bend strips to the hull if you just use pieces of wood glued to the hull then screw your teak to those. Construction adhesive works but lately I use gorilla glue for everything.
I like individual displays.
My Furuno had key pad problems after ten years. Furuno replaced the keypad, repaired it and upgrades the software for $500.
The hole is not round because that is how the pump works. Water comes in on the open side then the vanes turn and are compressed by the small side forcing water out into circulation.
Some pumps have a shoe to do the vane compression without the eccentric hole.
Ifall else ails you can retread the rod to SAE, not perfect but will work especially if the threads are similar in pitch.
I think the nuts should be bronze. If you can get a tap of the correct tread you could also rethread bronze nuts.