I didn't get back to the post on the original slotted head bolt till now. Stovebold, that '57 261 head has an oil line behind the pushrod cover coming from the rear cam bearing area over to the center head bolt area where on my running 261 there is a plug (and no line). Is this the plug you mentioned pre68 Dave? The slotted bolt reducing oil flow to the newer rocker arms makes sense as they look to be the same as my other 261 but why the oil line on one '57 head and not the other? Is my running 261 head set up to not need the slotted bolt w/ the newer rocker arm setup? I'm curious in case I ever have to start swapping things around. Thanks.