After I purchased these retainers via Comp Cams at Jegs, I am hearing that they are different? WHat is the physical difference. I am using these in a LT1 cylinder head.

 

Well I couldnt figure why the retainers, 774 didnt fit my LT1, as they just seemed to big for the retainers. Well, the LT1 uses a 11/32 inch valve stem, which is .3416 inches, and the LS-1 is 8mm (.3136 inches) . So if you want to use the Comp Cams beehive valve springs you need to order the 787-16 retainers which are for the larger valve stems. Hope this helps.