Just to follow up for the record, I ordered two Fatar TP60 keyboards from Arndt Organ Supply. Arndt will supply them with a MIDI encoder for each keyboard--at a very reasonable price. They include the cables that convert the Fatar connectors to the more standard ribbon cable connections. Everything is done for you, easy!
To make the Great TP60 fit I did have to cut down the plastic "feet" at the bottom of the keyboards. They caused the board to be a little over a 16th of an inch too high. I, with some trepidation, decided to cut these down and did manage it successfully using a Dremel with the circular saw bit. The swell keyboard was a bit trickier but fortunately the Schober construction is such that the extension on each side of the TP60s could be easily fitted in. I had to construct supports on each side that fit over the extension of the Great keyboard, just tall enough to give the Swell keyboard the correct height to fit. Bolting these keyboards to the console was the trickiest part! Not much room to maneuver but it worked out. Even though it didn't seem to be absolutely necessary I added a wood piece under the back of the Swell keyboard to give extra support in the center.
Daisy chaining the keyboards to the other encoder (pedals, stop controls and pistons) was easy. It worked first time.
The dimensions of the TP60s are not easy to find, if anyone is ever interested in knowing these give me a note and I'll pass them along. I can recommend Arndt Supply, they were very good and they make the TP60s easy to connect. You can see these keyboards on their homepage under "What's New".
Anybody interested in two old P&R keyboards, already with hours and hours of wiring and soldering into them?
Owner of an old Schober homebuilt, midified and Hauptwerkified.