Once you understand the workings of the hydrolic lifter you will understand why there are so many slightly different rods available.. The lifter "swells" to meet the length of the lifter. It operates there untill the wear gets to the limit of the "swell' available. When this limit is reached the thing starts clicking.. telling you to put in a longer pushrod...or do something to make the lifter work as designed again. If they are not clicking I cannot see how a slightly longer lifter would make it run better..
As for the cover gasket...NOBODY knows which head was installed in a particular year!!! period!!! About 1986 there were at least 2 different shaped cover gaskets. The one with the long straight side was the one that finally won out. It came with a plastic cover, not steel or aluminum.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />