305 heads have smaller intake valves than a 350, and the head volume is 58 CC instead of the 76 CC heads that are standard on a low-compression 350. The 305 heads bring the compression ratio on the 350 up to about 10.5:1, which requires at least mid-grade gasoline, or premium as a better choice. If you're ready to spend about 20 cents per gallon extra, go for it.
I use 305 heads on some of the claimer engines I build for round track racing, but I open the ports up for 1.94" intake valves, and 1.6" exhausts, plus some extensive porting and polishing. This type of head work usually adds $1,000.00 or more to the price of the engine, but it allows a racer who wants to bend the rules a little to claim he's running a stock 305 head due to the casting number. The head won't pass a teardown inspection, but the protest fees are so high at most tracks that the cheaters can get by with modifications that aren't obvious to the usual tech line checkout.
Jerry
