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

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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