If OP Brooks James is referring to the actual engine specs.....There was only one version of a 340 for each respective year, no different specs (except 1970 340-6 in T/A and AAR E-bodies). "FOUR BARREL", "MAGNUM", it was all marketing. MAGNUM was a Dodge thing, just like Dodge & Plymouth each had their own name for high impact colors even though they were the same and Plymouth E-body hood emblems were "'cuda 340".
RustyRatRod, YY1 & 1WildRT got the application details pretty well outlined.
Some confusion may have come from the fact that early Challengers were available with different versions of a 383 including the HP Magnum version. I'm sure 331IMP's friend has a 340 FOUR BARREL emblem if it's original.