Well, I suppose you could cut the fenders off but what about the ROP that mounts to them and you would have to cut out part of the floorbard also and since the MMM design is based on a 55 inch wheelbase with a particular spacing between tires then going to larger tires would keep the same wheelbase but the space between tires would decrease so it would not be possible to mount the belly mower. Also, the front tire track spacing is based on the factory dimension, a larger front tire/wheel assembly would interfere with the frame and thus limit steering so a spacer would have to be installed but then it would likely strike the FEL bracket.
No--everything really is not possible--a cliche I use also too often--but in this case it ain't possible or practical muchless advisable or cost effective. I suggest you trade for the 7500, even with the loss it would be cheaper than trying to convert your BX into a 7500. J