JIm your 1979 model MCI was produced into the mid 80's and still shares parts with buses produced into the 90's.
as for the MC_7 and 4107. there are no interchangable parts to speak of. as far as body.....you are much better of with a 4107 finding body parts, unless you can wait for an MC-7 to be scrapped out or are willing to put ugly and non complimenting fiberglass pannels on it.
really the only hard to oibtain parts on the 4107 that are not new or good OEM copies are the upper level windshields (astrolight windows).
the 07 shares parts with buses as early as the 4104 and through the end of production with the 4905
the MC-7 really doesnt share much with it's kin save the early MC-5's perhaps.