Mike, I'm guessing that was a "composed" set rather than something Winchester offered from the factory. That is, you just happened to have an extra set of barrels that worked. I had something similar many years back, except mine was 16/16. 26" IC/M and 28" M/F. On that gun, someone even checkered the wood.
One interesting fact about 24's is that the early ones with open chokes were factory C/M rather than IC/M. Or at least that's my deduction. I've seen a couple with low SN's marked C/M; later ones (higher SN) with open chokes all seem to be IC/M.
