Engine questions. Opinions are wanted.

[Mains52]

Ok dudes,
I have an 02' 5.3 right now I bought it for 400 w/ 170k on it. I started the stand alone harness my self and pretty much have what needs to be out..out of the harness. I am currently trying to trade my 4l80e for something that bolts up to the 5.3 without different this or that. Heres where I want some opinions for my questions.
1. I'm only wanting 350-400hp would it be dumb to just get rid of the 5.3 and grab an old school sbc or bbc?
2. If I keep the 5.3 would having a Muncie M22 be a decent trans behind it?
(A guy wants to trade an m22 for the 4l80e)
3. Do I just keep the 5.3 carb it for the ease of it and run the son of a gun?

Thanks in advance.......I think!