I recently put a set of Hedman's on the 318 in my '75 Duster and couldn't get them to stop leaking. I've used stock gaskets on sbc's,fbc's, and fe's before with no problems. I solved the problem by buying a tube of muffler repair ( $1.99 at O'Reilly's ) and laying a bead of it on a new set of stock gaskets around the port area on each gasket. The stuff glazes over in a couple of minutes, but doesn't cure for a couple of hours. I let them sit for about 10 minutes, installed them and tightened everything down. Fired it up and walla, no more leaks, at least not at the heads. Ended up doing the same thing with the collectors. So far,so good.