66 350 open letter valve cover gaskets. been thru sveral sets of gaskets, all fresh and new, fel rpo, napa, no cheap ones and none fit remotely close. best found were the black rubber thick ones and trimed off the tabs. these are the original covers, un warped, never a leakage or fit problem, lst ones been on since the 70's, factory new ford service replacements. what are you using? stock original motor. I am aware of the problems with old nos gaskets shrinking and warping. what was the original gasket like? material, tabs,etc. thanks, phred