The cone on the transmission side shouldn't make any difference. The 381066 disc is 11", correct? I have not called M-Pact yet, I am thinking about trying an M-Pact 384195ST1, it's a 12" diameter 10 spline 1.125" disc for a 1993 Chevy/GMC 3500 that appears flat on the flywheel side. I want to see if it will work with the 3 lever 12" pressure plate that comes in the Platinum/M-Pact 04528.
https://www.rockauto.com/en/moreinfo...=10605&jsn=648