working from a stock longblock with the heads you mentioned (68 302 castings had 4V cast into them), you should have compression somewhere in the mid 9's. What you need-cam with around 225-230 duration at .050, lift around .510, preferably dual pattern with more lift and duration on the exhaust. Go ahead and swap over to a double roller timing chain while you're in there. The cam will come with new lifters, and make sure to get new valvesprings as recomended by the cam manufacturer. Be sure to check the installed height of the springs, it can make or break a cam swap. With the cam in, swap to a performer rpm or weiand stealth intake. For a carb, take your pick, something in the 600-650 cfm range will be fine. I'm partial to double pumpers, doesn't matter though, edelbrock, holley, demon, they all will need some tuning to get just right. For exhaust, I like Hooker Comps with the ceramic coating, coupled to a 2 1/2" exhaust with H or X pipe and some good flowing muffs (magnaflow, dynomax, flowmaster, etc). With everything proerly installed and tuned, you should be right at 300 hp. Roller rockers are nice, but you'll have to remove the heads and send them to a machine shop to have them fitted for screw in studs and guideplates($150-200), plus you have the additional cost of the rockers ($200) and hardened pushrods ($80). It is money well spent, but you can do without it. 300 hp can get an early model into the 12's with the right driving and good traction.