Faster is on it - these boats were almost entirely tiller boats, wheel was not likely even an option from Hinterhoeller back in the 60's unless someone insisted, so it could be after market. If George was still alive I'd drive over and ask him.
View it as a tiller boat. Rudder inserted from below into the tube, through the stuffing box/packing gland, through the cockpit sole and through the cast aluminum bearing plate that is fastened to the cockpit with 4 screws. Hole in the top of the stock would be for the original tiller to connect. It was a simple design, so keep it simple.
You have the quadrant disconnected, there is nothing clamping the stock above deck. In theory it should just drop out. I'm understanding the gland is fastened to the rudder tube similar to a driveshaft packing gland - rubber hose, hose clamp(s), other end of hose clamped to the bronze gland (Perko, Buck-Algonquin), shaft comes out the top end headed north. Gland screws together like a lid on a jar, should have a locknut on it too. If that is all loose/removed there should be travel. I'm thinking environmental corrosion, disimilar metals bonding, maintenance neglect over the years, likely near the bearing plate cause that is the primary entry area for salt water, dirt, etc.
When you force it, does the shaft rotate in the bearing plate on deck? Have you removed the screws from the bearing plate? Does it rotate freely now? It could be frozen there.
You might want to contact Bob Reese (he could be in FL for the winter) at Beneteau, Back Cove Yachts, Sabre Yachts, Used Boats, J Boats, Dealer for Sailboats and Power Boats, Parts, Services, Financing
- They were volume dealers for Hinterheoller and Bob or someone in his shop might have your answer, a drawing, or some other advise.
This is a simple boat with a vexingly simple problem.