Otherwise, I think I'm on track with superflow valves, Kibblewhite springs, Dynoman guides, 392 78K head, Kenny Harmon D grind (DP117KHD), which appears similar to the 125-00, stock bore, Ken Augustine head work, including "mild" porting, HD case/cyl studs. A bit concerned about getting a good pre-oiling pressure before start-up. Just changing the oil with a new filter takes about 15-20 secs of dry (no pressure) spinning.
That does seem a little long if the engine is already 'wetted'. There's a few things to check for this:
1. The O-rings (2.5x15 size) on the little dowels that align the oil pump into the crankcase. Make sure they are new, and springy, so they seal well.
2. The aluminum seal washers on the inside of the oil hoses were they screw onto the tank. If you haven't disturbed the hoses by unscrewing them, they are fine, but if disturbed they often need to be replaced to seal well.
3. The 2.5x15mm O-rings on the 2 oil hose castings that bolt to the engine. Heat has usually hardened these and they should be replaced often.
4. Inside the oil pump: the #1 leak site is the seal on the shaft between the 2 impellers. You can still get this seal from Honda (look at the GL1000 Gold Wing oil pump, same seal), even though it is not listed for the 750 anymore. It also fits some outboard engines, fortunately, so will be around a while. There are 2 O-rings 2x46mm inside the oil pump covers, too, but they seldom leak.
I have seen this sort of difference after replacing all the seals at once: an engine that took 5-7 seconds of idle speed (1000 RPM) to turn off the oil light changed to about 1 second off on the light, after a full oil change with filter. Pretty dramatic change!