Lt1 350

i have a 71 lt1 350... how much hp gain would i get if i port and polished the heads?

About 15 hp... If you want more, change to a more aggressive cam and performance rockers.

yeah the motor was rebuilt with a bigger cam and everything is built just right im gonna get some rollers for it and port and polishing is the only thing i can think of that wouldnt affect the valvetrain in a negative way

Get a set of 10 year old circle track heads from an old engine builder. You want hp? You can easily push 500 hp with the right set. My father builds engines with flat top pistons and flat tappet camshaft that put out over 500 hp. Having your heads opened up in the ports will get you some hp, but most heads are cut on c&c mills these days. Very few folks still hand porting. You'll get bigger valves this way, and you can always go back to the stock heads for a picky buyer.