Wayne Brewer at Brewers Performace set me straight. When I pulled my clutch out of my 273 hipo, it was a frikin 9 inch clutch meant for a six cylinder. I am now running a 10 inch clutch with the SAME bell housing and flywheel ! He called it a 'bastard clutch' and it works by notching the plate, and installing with special screws. The plate is also a little taller, and now my pedal is back the way it should be. NO slips or vibration to 110 mph.
By the way, it took me 5 hours to stab the HEAVY, awkward, 833 trans back in......by myself.