If you have a GM cover I have been using .008 paper gasket. The HV kit comes with 2 gasket of different thickness. I don't use the HV gears just the gaskets. If you have an aftermarket cover the thinest one you can get,that would have to be from TA. The gears are recessed on all aftermarket covers that I have used. GM's are above the cover. Another VERY important area is the side clearence. .003 is where it should be. If the inside of the cover is all grooved up it maybe be better to get another cover. GM is about $200 if it's not discontinued.