Jon, I'm working on designing a machining fixture that can be used in a low speed drill press tall enough to stand the block up under the power head to cut the counterbore for the full circle lip seal. It will be a high speed steel shell end mill 4 3/4" in diameter, with a ball bearing support that centers in the main bearing bores. The cutter will have about 20 cutting edges, so it should cut an accurate counterbore with one pass. Then all the machinist would need to do is make the cut in the block and the main cap the correct depth. The cutter would be a bit e$$$pensive, but it would pay for itself in 4 or 5 jobs, and it can be resharpened without changing the OD of the cut.

Here's the seal, one of several with the correct dimensions that are available.

https://www.motion.com/products/sku/01315653

Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!