I think the concern of starving the seal will take care of itself. Let's think about the U channel. If you study the crankshaft, you'll see it bevels where it meets the part which is the crank sealing surface. In fact, blow up the image I attached to my post and you'll see it clearly. That means any oil that runs out of the rear main will run along the shaft to that upward facing bevel and be slung straight out radially. That bevel will actually streamline the radial slinging because it minimizes the amount of direction-changing the oil must do. So all the oil runs to the rear side of the U channel and bathes the sealing area. Even with a .001" bearing clearance that will not be a small amount of oil although if the bearing clearance is .003" or so, the amount will become notably more. At .005" or more we're talking an abundance of oil.
The oil present on the sealing area is enhanced by the natural slope of any of these engines when in the vehicle. In fact, due to the design and orientation of the U, oil that lingers in the U will be continually present on the sealing area.
The Speedi-Sleeve orientation is the opposite. The bevel will be on the inside (facing the rear main bearing) and that will slow the oil down a wee bit as it changes direction. Then it or any slinger with a straight vertical edge will sling oil radially, but this time if the slinger was set so it was as close to the rear edge of the U as possible without risking interference then as the oil was slung up into the U channel oil present on the sealing area could be reduced as long as the U wasn't filling up with oil all the time. And conversely I think if the slinger was set as close to the front side of the U channel as possible it would limit the amount of oil that could pass by the slinger on to the back side of that channel. But given the slope of the installed engine, I can't imagine that a slinger would eliminate oil present around the sealing area...minimize it, yes that is the hope here.
But here's where Jerry and his knowledge of things like this will be necessary, so hopefully he'll add an opinion.
