You caused me to go back down the basement and measure my disc. A #35 drill bit [.110"] fits between the rivet heads and the straightedge across the friction pads. No way those discs you have are going to work with a Pontiac flywheel. You may be falling victim to the 'GM is all the same' mentality. I have had good results with Borg Warner discs, but last time I needed an 11" 21 spline disc for my ST-10- no one had one. I ended up getting this disc from an actual clutch re-builder that used to be in Jamaica, Queens. It looks very meaty. If you are getting 'GM' discs from parts stores, maybe search for a new disc from a name brand company like Borg Warner, McLeod or Ram. And as big of a PITA it would be, maybe take your flywheel along and only purchase a disc that has the clearance I got.