300hp is very attainable, 350hp isnt that far off. But dont think headers, intake mani, and some trick ignition with bright colored plug wires will do the trick. Hp from the 305 comes the hard way, heads and cam. World products torquer 305's are good heads. But if you on a budget corvette aluninum 113 heads, and theres a cheaper, iron version that i cant remember the casting number. Both heads would work on HO and normal 305s One last head choice is l31 vortec truck heads, can be bought from gm for 400 a pair, fully assembled. And obviously you would need a votrec mani. Also cam choice is important an comp xe262 or 268 would be real radical, this lunati wouldnt be nice and mild in a Daily driven 305
http://www.summitracing.com/parts/LUN-60101/ But "yeah blah blah get a 350", all the parts can transfer to a 350, the heads would need to be put on a 350 shortblock with dished pistons though, not too hard to find. The two comps i listed would still be nice and lumpy in a 350, but cams are cheap enough that you can buy another one when you wanna upgrade. So in the end with those parts 300-350 crank horsepower on a 305 expect 350+ on a 350.
