I agree nothing to do with emissions imo but more of a move away from the pretty awful Biturbo era reputation under DeTomaso. The Ferrari?Maserati engines have been pretty good though to be fair.....
More than likely it was dropped to get away from the "Biturbo" era and reputation and also to put their mark on the car. Ferrari's at that time and are still mainly about the NA experience. Did you know that the 4200 lump was actually a Maserati engine with Ferrari input and then later used (with slight differences - flat plane crank and tweaking) on the F430?
alway thought these were Ferrari engines, telling people it had the 430 engine, so what should happen is the 430 guys should be saying this has the 4200/Gransport engine
the F430 engine sounds high pitch (like most ferrari's) great sound, were the 4200/Gransport has a lower pitch - I see member trying to get the sound released from these engines but could be missing your point, maybe need to look at the crank and other tweaks.