Lenie, if budget weren't a concern I'd go LS7 all the way. I am biased though towards the LSX motors.
I think your car would be killer either way though, not too many Birds done to the level of yours so at least it's different.
Here's a couple videos that may sway you in the LSX direction
:
https://www.youtube.com/watch?v=RxEgUMZqJbE
https://www.youtube.com/watch?v=el6t9I5TvjA