My 2002 Chevrolet blazer currently has a 4.3L v6 vortec in it, what would I have to change to put a 5.7L 350 vortec in?

 

There's a ton of information out about V8 swapping S10's and the like, most of which could be found on v8s10.org or even s10forum.com or blazerforum.com

To make a long story short however:

You'll need new mounts, headers, exhaust, and possibly a new transmission crossmember to fit the exhaust.
Also, are you 2WD or 4WD?
Do you plan to keep the Vortec fuel injection or are you going to go carburetor?

This particular swap has been done many, many times. The info is out there, my friend!