My understanding is that if you have a flywheel that will accept an 11 inch clutch plate, you have the heavy duty clutch set up. I have never actually seen one of those flywheels but I also understand that those set ups take a somewhat unusual pressure plate, which your post seems to confirm. If you are having trouble replacing the clutch or pressure plate, you might consider having your current parts rebuilt. HR Clutch in Bensalem pa still rebuilds these kinds of parts.

http://hrclutch.com/antique-clutches.html

Old school shop, reliable advice, can rebuild those parts good as new.

Mike