RCDs & M3 75mm GMC?

[Dave Block]

First up, thanks again to all who replied so far! Attached is the RCD photo from LAC that I alluded to in my previous post. The second is the one kindly provided by Wim Sikkelbein showing a vehicle in Holland. Something kept bothering me about the latter photo and I realized the fenders are very odd. The M3 75mm GMC was built by AutoCar and should have 'standard' M3-style rounded fenders. This one has the flat-profile M5/M9-style fenders! Could the base workshop lift the whole 75mm assembly out of an otherwise clapped-out M3 and plunk it into an IHC M5/M9? The firepower of the GMC seemed to be greatly appreciated and this is the only explanation I can think of for the obvious fender difference. The orginal M3s had two previous owners before we got them so I can see the vehicle needing replacement before its 'gun'. Any thoughts & insights would be greatly appreciated.
Cheers, Dave