Some time ago, I worked on a mecha game for Swords & Wizardry called Lorica. I avoided talking about heat because that was something that always frustrated me in Battletech.
Based on the inspiration from this post, however, I think I have a way to include heat. I haven't worked out the details yet, but I'm sure it will be heatsinks to heat production with each to hit roll adding to the heat meter. Go over the meter and roll a save to avoid overheating.