Well, with my own experience, I would say: NO! Don’t let them together until Bell is neutered and it has been 5 weeks or so. Not even supervised.
It seems that they get on so well right now, so it would be such a shame to ruin it, and you end up having to spend the next couple of months doing bonding sessions in order to make up for some small tiffs due to hormones.
But well, every bunny relationship is different, and yours might just be able to deal with Bells hormones. But I introduced Freddie way too early after his neuter, and it wasn’t the fact that he was humping (he didn’t), that got him and Karl into fights. It was the fact that he insisted to sniff Karl between his leg. This made Karl so angry, and they were actually getting on really well up until then. And now I have two males that have a rather tense relationship and I have to spend time bonding them. If they had not meet before 5-6 weeks after the neuter, I think they would have bonded instantly, because there was in fact grooming between them on their first encounter.
I know some people say unneutered males will fight to the death or even castrate each other. I’m not sure about that, but even small tiffs are horrible if you want them to live together in your household. So be patient.