340 heads on a 318?

good 340 heads will lower your compression. You would need new pistons to bring it up or have the heads milled. I would suggest new pistons as head can only be milled so much. Another choice would be to find some 360 heads with 1.88 valves. they were designed to flow better with the 8.6 compression your 318 has. not to mention they will be cheaper than 340 X heads. take the money you save on the heads and get them polished and ported. Your 318 will thanks you for it.