It would do fine until the convicts started breeding and then they would try and kill anything they think poses a threat to their young. IMO i just wouldn't do it just to be safe.
I would go for it if you've got a big tank we're talking about widthxlength footprint here, poly's could take up a beating and will tolerate it. They're peaceful monsters not unless they see you as food, some of the guys here has a couple of convicts in their tanks and let em spawn in the tank so that when it's nighttime the polys will eat their young in order to control it. But as Dr. B said it, I wouldn't go for it specially if you're down to 65g.
should be fine, I kept a pair of convicts in a 30g with 2 small senegals with no problems, when the convicts breed they'll drive off the bichirs if they try to enter the cave they are nesting in, but the bichirs just move and sit elsewhere and then the convicts left them alone.
They will eat some of the babies but convict's are smart, the young will remain hidden protected by the parents at first , by the time they gain a bit of size and venture out to explore they've learned to avoid the bichirs. I still had to clean out tone of juvies and they made excellent feeders for my other pred tanks because they arn't easy prey so the fish have to really work to catch them!
Seems like they would do good together but you really have to watch the convicts and if they start breeding to either remove the convicts or the poly (i'd move the convicts because they can do way better in a smaller tank that a poly can).
The tank i housed them in was aa footprint of 36" x 12" both senegal's were about 5" at the time, both convicts were large full grow adults. if your very worried just include a rock/piece of wood, that the bichirs can hide under but the adult convicts can't, Or a piece of PVC works well. But i dont think it'll be a problem, being bottom dwellers the convicts tend to ignore them. Any mid/top level fish would catch those convicts attention and get killed but my bichirs had no problems. will help to place the breeding area out of the way as well, they'll protect about 12" all around it and wont leave that area while breeding, Stick the cave right smack in the middle then ya the bichirs might keep crossing paths with them more often but if you stick it in the back corner and leaves lot's of floor space for the bichirs to live happily