Purists look away.
Missile Command originally uses 8 x 4116 rams, and 4116 rams are terrible. They don't just die (a lot) they often take out other parts when they die. It's best to replace them with 4164s which run a lot cooler and are far more reliable, they also don't require +12v and -5v like 4116s.
It's already common practice to replace them on Williams boards but doesn't seem to be so common on Atari boards, not yet anyway.
Since there's no tried and tested mod for Missile Command I spent some time looking at the board to see the cleanest and most reversible way of doing the modification. You can mod the ram itself but this looks awful and not practical for some collectors to replace them where as anyone can drop in a stock chip.
Here's how I did it.
The cuts need to line up with the via on the back of the board where the 12v and -5v come through, if you hold the board up to light you can see it a lot clearer and mark where you need to cut with a sharpie.