What to upgrade first?
 

79 k5 blazer, 350 small block gen 1, 4 barrel eddlebrock 650 carburater, 3 speed SM465 trans.

I know I want to put a supercharger in my truck to make it a super sweet off roader. What upgrades to my stock engine do I need to make before getting a supercharger? If I need to redo the entire internals of the engine, would it be more beneficial to do an engine swap rather than a rebuild? I'm considering the ls3 , which is what is currently being put in the brand new Chevy and gmc trucks, to make it fuel injected and give it a tune. Thoughts and ideas would be greatly appreciated!

If you have the resources, an LS swap with a 4L80E is definitely the way to go. Better power and economy stock for stock and can always build it up if you want more. Huge aftermarket support.