A big male JD can easily attain 10-11ins. That leaves not a lot of room in 75g. That said, you can never predict what will work and what wont with compatibility. I have had adult male JD that were good community fish, but in 200+ gallon tanks. My current male is 6yrs old, about 10ins and as mean as they get. He will accept no tankmates of any kind, any size in any size tank. In 75g with even a bit of attitude, I think odds are high that JD will kill most anything else. Imo, a 75 g tank is full with any aggressive cichlid in the 10in range.
Mine is only 4", female. Have 2 bristlenose plecos, she doesn't bother with them at all. Also have 2 corys. For the most part she ignores them, but if they come near her hideout, she nips at them. Who knows if she will eat them when she gets bigger.