[Clyde65]

Here is another thing with the LSx swap.

5.3/4l60e, cam, tune, headers and CAI. You have about 375-400 HP and 18mpg.

SBC will be hard pressed to get that.

I run a 4.8/4l60e and I only have about 325hp and get 20mpg regularly.

I have somewhere around $2500 in my swap give/take.
Have had it for 7 years and can run 80mph if I want to. Ac/cruise
Good luck with whatever you choose to do.