What's massive? I would call anything over a foot "massive" (but then again, this is "monsterfishkeepers.") Using my definition of massive, what about:
L007-Galaxy Pleco: 10 inches SL
L114- Leopard Cactus Pleco: 10 inches SL
L264- Sultan Pleco: 6 inches SL (3+ of these as they are supposedly gregarious)
These all are "carnivorous "plecos with teeth, so I think they could hold there own with these chiclids. (Though they are carnivorous, some vegetable/fiber in their diet may help prevent bloating)