HEI in Mopar ECU casing

I understand the current plan, but let me run something by you.
If you have a heatsink for the ECU you don't have to mount the ECU to the firewall.
You can leave the ECU and heatsink floating so to speak. (as long as you have a ground wire for the ECU it does not have to be mounted to metal.)
You could also use the firewall as a heatsink and ground and mount the ECU with the thermal compound between them.

Just some possibilities that I didn't know if you had thought of yet.

Well, do you think the heatsink I have will be enough by itself? Its 1/8 thick aluminum. And is about 3/4 the size of the front of the original mopar box. Look previously in this post for pics of it, only I ended up using just the one piece instead of stacking. The 2..