I posted what follows a year ago, Alan. Also, last summer I had an acquaintance install three (!) of the neoprene seals in a 312 before finally having success on his fourth try with a rope seal.
NoShortcuts (4/24/2013)
Many years ago, I had the experience of fixing y-block rear seals on two different engines. I say 'fixing' because in both cases the full rope seal was not replaced!
The engines were in vehicles. The oil pan was dropped (after disconnecting the oil pick-up tube to the oil pump), and the rear seal retainer was removed. The crank assembly (main bearing caps, etc.) was NOT disturbed in any way on either repair.
Two steel shims of equal length (just short of 1/4 the diameter of the crank rear seal area) were tapped into the cylinder block upper seal retainer groove between the rope seal and the retainer groove. The shims were pushed in until they were flush with the edge of the upper rope seal end on each side of the upper retainer in the block. These shims served as wedges to go in back of the upper rope seal to force it against the crank seal surface. The shims were made from commercially available spring steel strips, were approximately .060 or less thick, had a width of approximately 3/16 inch, and the ends that were tapped into the upper rope seal retainer were shaped so as to have somewhat of a bullet shape profile. Also, the lead edge of the nose of the shims, the ends tapped into the upper rope seal groove from each side, the edges were slightly tapered and rounded with emery cloth so as to not catch on the rope seal edges as they were tapped into place. The steel shims were tapped until flush with the block mating surface for the removable aluminum lower seal retainer.
The lower rope seal was replaced in the lower removable aluminum seal retainer per standard repair manual procedure and reinstalled per the same repair manual. After cleaning the oil pan, servicing the oil pan bolt holes, replacing the pan gasket, and reinstalling the oil pan and reconnecting the oil pump pick-up tube you'll be done except for adding engine oil.
In both cases, rear seal leakage was stopped. The rear seal repair was immediately successful and final for the customer.
I'm told that farm equipment suppliers had this type of rope seal replacement 'kit' available for use on farm tractors at least back in the '60s. The first of the two y-block rear seal repairs I did was done with one of these farm supply provided 'rear seal repair shim kits'. The second rear seal repair I did was accomplished by making and using the shims I've described.
Hope this helps.