1978 911 SC flywheel dimensions and clutch troubles

[tonypnz]

Hi all, my car's clutch was slipping a little under hard accel, so i purchased a Sachs power clutch and replaced. Only lasted 2 months, on first track day ripped the linings off the plate. Had a spare paddle clutch, so threw that in to get mobile, that lasted 2 days before melting the lining to the friction surfaces! Pulled clutch back out and took to clutch specialist. He has tested the original slipper, the Sachs power and the paddle and says that they are going over center on the pressure plate springs, he thinks due to the flywheel being turned flat and believes there should be a 1.5mm step in the flywheel for the pressure plate to mount on.

My question is: Can anyone confirm that there should be a step or suggest a place to find dimensions?

Cheers in advance