HEI in Mopar ECU casing

I don't even know if the GM module has a bare metal area on its bottom for heat dissipation. If it does, a heat sink compound could, if not should, be applied to any mounting surface. As for your screw showing concern... they wouldn't show any more than what is shown on your bottom plate.
I'm not saying "I see fault in what you've done" or trying to build a better mouse trap. Just coffee talk.