ok i would bore it out, talk to your machine shop about how far over you will be able to go, also you might want to see about getting some heads from GM perfomance, i think summit sells some for $500 i think they are vortec heads but im not sure im a ford man but some of the other guys on here will know. but you could get some headers, just call summit, dont go crazy big, anything with 2 1/2in collectors should be fine. then you will want an intake, prob something with a high rise, you wont be worried about torque with a 305 i would look at edelbrock, as for a cam look at comp cams i would get something with about .480 to .500 lift and .200 to .220 lift @ .50 there should be a measurement @ .50 that is what you want to look for, not advertised duration. i would put in some 10:1 compression pistions, and make sure you get some new valve springs to handle all that valve lift, comp should be able to sell you everything you need