What year and combo to look for?

Not sure it makes that much difference except........

If you run a stick or a non-computer controlled automatic, you want a stick shift ECM

And don't get one that is locked out with the security stuff.

There are "folks" who can reflash them for a price.

Magnums are getting harder and harder to find as "ready to run" "low mileage" pulls. How long ago did Ma stop makin' em?