I just found out that I have the wrong rear seal retainer.  I have an ECG-6335-A, and think I need an ECZ-6335.  There is another 312 engine at my machine shop and we compared them.  The ECZ has a larger ID and wider channel for the seal.  The part number on the ECZ seal is not clear.  Are the billet retainers better than the factory aluminum retainers?  I also only have 1 12 point bolt, I assume the bolts for the retainers are all the same.

Thanks, 

Paul J. - '57 E Code