What do you think about adding 350 vortec head to a 305. I'm looking at try to get 350 horsepower on the crank and running nos too.

 

If you're gonna do that, have them milled 0.030" and use Fel-Pro steel shims, p.n. 1094

 

Will i have any valve clearance if i change out the cam?

 

If you want 2.02" intake valves, you're limited to about 0.400" valve lift with the milling and 1094s. If you keep the 1.94s, then you can go way too far on the cam before your valves touch anything.

 

What is a good cam? I dont want to have a very big loop and i'm like to use a 150hp shot of nitrous.

 

Better use a progressive controller if you want your stock pistons to survive a 150 shot, 125 is good for a 350, 100 is better for a 305.
As for which cam, it's near impossible to choose wisely without knowing the rest of your combination. Since it's just a 305, probably COMP's Nitrous Xtreme 262H

 

Stock bottom end, 350 heads, 750 cfm carb, 1.5 rockers thats about it

 

Then forget ANY nitrous until you get headers and a cat-back.

 

Why , I was think that i might have to change the exhaust manifold but that is it.

 

You have the low-perf exh manifolds. These have 1.87" outlets. These even restrict the base 305s. The HO V8s has different EMs that had 2.2" outlets. better, but on a 345 hp 350, they still cost 37 horses.
Also, you have a single 2.25"-O.D. exhaust system that's also a restriction to even the base 305s. The TPI 350s had 3" exhaust.
What you have is already limiting what little power your lame 305 can offer, you can't really expect a 350 or nitrous to help if your exhaust won't flow well enough to support more. That's why the exhaust system is always one of the first 2 mods suggested. (The other is subframe connectors)

 

Ok thanks I will look at getting some headers and exhaust work do