This thread has delivered, thanks everyone!
It is an iron block 4.8, whatever engine code that is. Sorry for any confusion.
I do love the idea of a high-revving, small displacement v8, but also dont want to always have to be north of 5000rpm to make power. Since the motor is apart, I plan to do LS2 timing chain/gears, and replace the valvetrain regardless, since it's a 'while you're in there' insurance policy for me.
What I think* is my best path forward, given all of your input, is-
Stock heads with minor/mild porting
LS6 intake (need the clearance)
Ls3/LS7 springs/rockers/pushrods
A cam that'll get me the rest of the way, with a nice flat powerband from something like 3-7k... 7200ish redline.
Custom intake and exhaust (It's a swap, so sort of necessary anyway)
Professional tuning
That sound reasonable for 350ish whp? Please nitpick away too, you all are awesome and I really sincerely appreciate your input. Thanks again!