You keep the 8 1/2" flywheel, but use a clutch disk from a early/mid 80's Ford 4cyl car. I have the specifics on that clutch disk. The pilot and t-out are from a '67 and later 6cyl 200 car.
I'm not sure this is the problem, but did you have the pressure plate mounting surface of the flywheel machined the same amount as the clutch surface? It's the recessed flywheel (the one in the top left of the pic)
http://pages.prodigy.net/al.martin/200Clutch.jpg
I've heard of that causing problems with clutch slippage.
I make and sell the plates for $120 + shipping. It insludes the hardware in the pic. I machine each plate individually and pay a machinist to cut it for me.
http://pages.prodigy.net/al.martin/303.JPG
I currently don't have any made and the machinist I use recently lost his wife, and is also extremely busy, so I'm not sure when I can get another one cut. I'm trying to get a few done so I can stock them though.
Al