I'd say you'll be fine for awhile as long as your not beating it hard everyday. I the meantime you could look for an 8.8 rearend out of an Explorer. Typically cheaper then the 9" rears I've seen and a better chance of finding one in the junkyards.

 

I agree, you'll be ok with the 8" for now. Your not going to be on the track first time out anyways. Just keep it on the list of things to upgrade and you'll be fine. Don't panic with the thought that your going to blow it up the first time your drive it. Besides, the upgrade list, will always exist right?