Gary, I don't know that I'm 100% correct on this, but I'm almost positive that the standard camera tripod screw thread, as well as the female thread in the bottom of the cameras to mount to tripods and other accessories has always been 1/4"-20. That's the standard SAE 1/4" coarse threaded bolt/nut you'll find in any hardware store. If I was at home, I'd check it out for you to be sure.
If you can find 1/4"-20 threaded brass inserts (the kind where you drill a slightly larger hole in the wood, and screw the coarse external threads of the brass insert into the hole, leaving you with useable brass internal machine screw threads), you should be able make up a plywood platform or other kind of wood fixture to attach to the top of the tripod. You could use the T-nut style of internally threaded insert which hammers into the hole, but they don't have as much strength in tension and can pull out of the wood easier, IMO.
Hope that helps.
Bryan