Well I don't think it should be cracking the bell housing in the first place. I've been racing for 25 years and never busted a trans case. You've got a real problem if you are. Do you have sub frame connectors or a roll cage? Sounds to me like you have way to much chassiss flex along with not enough flexibility in the mounts.
If go to an ultra bell you may still brake something just in a different location, so your just covering up the problem and transfering it to the next weakest link. Just my $.02