Does anyone know ignition modules well ?

Well they are not, exactly. There are some OEM are supposed to be better than others, the "legendary" orange or chrome box. This is OEM not aftermarket.

But 5 pin boxes will not work in a 4 pin situation

The deal is this:

You can NOT tell a 4 from a 5 pin box by looking, because many 4 pin boxes have 5 physical pins. You must check resistance between all of the pins to determine if the "5th" pin is open/ disconnected

a 5 pin box MUST have a 4 terminal ballast. A 4 pin box can work with EITHER a 2 or 4 terminal ballast.

The "good" news is that nobody has made 5 pin boxes for some time. But you may run into a NOS one

The "bad" news is that all aftermarket auto parts "today" are pretty much junk. All poor quality, and all Chinese, all the time.

Looking to purchase a replacement ICM for my car (72 Dart 318) it has a 2 pin icm and all I see on Rockauto is 4 pin. Will a 4 pin work on my car?