Upgrading stock 1971 318 heads

Yes, the exhaust ports will match perfectly with 340 manifolds. Use 360 exhaust manifold gaskets. 302 heads are usually close to 69CC what year heads did you originally have on the engine '71 318 heads???

Treblig
yes original stock 71 heads. so at 69cc would milling 0.40 not allow me to run on pump gas?