If you go to the speedmaster website, it says that procomp is the sole US distributor for speedmaster.
So speedmaster is procomp.

I can't speak about the SB mopar heads, but when the Sidewinder BB heads were first being talked about, one of the owners of the foundry in china confirmed that at least for the BB Mopar head that it was the same head as the ProMaxx head.

I just received a set of speedmaster BB mopar heads, and I can see no difference between these and the Sidewinder heads. They even came in the same looking box.

My guess is, the speedmaster/procomp/ProMaxx SB mopar head is all the same casting.