It's semantics. The common term for this part on an automatic transmission vehicle is the flex plate because of its lightened and flexible nature. On a manual transmission vehicle, it would be the flywheel because it has a much more substantial rotating mass.

 

Anybody know when they switched from stamped to aluminum oil pans? They interchange with each other? Do the aluminum ones have an oring or gasket type seal?

Oil pan is a pain in the *** to remove BTW. My be an older engine with the older pan. I think the aluminum pans have slightly bigger threaded bolts.