What would it take to get 325 HP out of my 1988 350 Blazer ? I think it presently has 210 HP.

 

I believe Edlebrock has a package that will get your engine in that neighborhood. Involves replacing the TBI and manifold plus the heads and cam, IIRC. Holley may have basically the same product.

From what I've researched over the years, the TBI has to go, though its been a while since I looked anything up. Probably the easiest and cheaper means would be to go with a performance crate engine.