kj5kb
KEEPER OF CATS, FISH AND CATFISHES
I have 3 ~2" BN plecos in a 20H and they are fine together. I have another in a 20H planted tank with no problems. I would think you could easily have 6 in a 75G if there were plenty of hiding spaces...that's where mine are headed 
Just make sure they are Bristlenose and not one of the larger species.

Just make sure they are Bristlenose and not one of the larger species.