That mower is for a BX series ...... so a direct bolt up probably will not work.
IS that the deck that has the drive over rail on it?
Having said that - almost anything will fit IF enough modifications are made.
I would say if you are getting it close to free - there might be a way, but having to pay a lot for a MMM and then have to weld and rework all the linkages, could be a real PITA.
I have a B7100 that someone placed another deck under - I did NOT know any of this when I bought it, once I did a little homework after the fact I found it to be a different deck that had some things modified to make it work.
EDIT:
info found :
B7500 HSD came new with the RCK60-24B mid mount mower deck. The Operator's Manual for the mower lists the following "suitable" mower/tractor combinations: RCK60-24B & RCK54-24B mowers suitable for B7500, B7400, B7300, B2410, B2400, B2100, and B1700 tractors. RCK54-75B mower suitable for B7500 & B7400 tractors