For what it's worth, I did have several reasons for jumping the gun and getting the Juv Imp.
1. I am upgrading to a 240-300 gal long before the juv becomes adult.
2. I have seen lots of literature indicating that as long as the angels are different genus and appearance and size, it should be ok.
3. I already have 2 alpha-type fish. The passer is not the king of the tank, the powder blue tang unquestionably is. I have read numerous places that in terms of conflic avoidance, 3 is better than 2.
Keeping an eye on things. Thanks for the feedback