Gary,
I think your thought process has been good on this from the beginning. It is the little stuff that you don't want to get caught out on.
I only have a theoretical negative reaction to piping pressure into the crank case. It just seems so wrong! In reality it may be fine.
I don't think I ever put that much oil in a D oil tank, but on the C racer after a complete change I only used two quarts in the tank. I often ran with less. A two thirds full tank is what I designed for on the Egli frames I built.
Pat Manning is not here, but when I opened his D oil cap no oil is visible and I seem to remember that is what I did with mine. "Fill it until you just can't see the oil." It does sound a little odd, but I stuck a plastic flexi ruler down the filler and I hit the oil at 4" down from the top of the filler, which is about 2" down from the top of the tank. I will check with him also.
I think if you can fill it higher like Mcvette does, that is fine. I think more room in the tank is nice, particularly if you have some oil in the sump. You need some room in the tank for it. You might want to do some trial runs to see what you are comfortable with and some other D owners might chime in. I will ask Carleton Palmer who has been riding his D a lot lately.
David