I found the problem. Quick update then getting a bite to eat, cleaned up, then hitting the road.
The shafts were new, detailed several pages back when I used new HS shafts and factory adjustable rockers.
Here's a picture I posted of what I used...
You can't see it in the picture, but there was only a single small oiling hole on those shafts for the rockers. Smaller than the single hole, non-grooved original shafts. The rockers weren't tight, they seemed about right on the shaft although I didn't measure.
First, I tried switching to 10w-30 oil, but there was no change. I took a probe light and peered down under the intake, but it was difficult to see much with the valley tin in place. Still, I could see oil flowing over the lifters, but not gushing anywhere like you'd expect to see if a plug had popped out. Next I pulled the necked down bolt out and cranked the engine over. Lots of oil coming out of the stand then, so I immediately thought about the shafts. Then I remembered about that small oiling hole, which I didn't like at the time when I was assembling them, but I had used HS shafts before like this without issues. I looked on my shelf of parts and found a nice set of old shafts that have the groove in the bottom hole and a second hole towards the rear of the rocker. Knowing that old shafts can hold a lot of crud, I went through 6 cans of brake cleaner and LOTS of air pressure before all the brake clean ran out clear and no crud was coming out. You'd be surprised at how much crap those shafts can hold! I assembled all the rockers and stands on the old shafts and reinstalled one side, cranked the engine over, and BINGO, I had lots of oil oozing out of the rockers and down the pushrods. That seemed to cure it! I did the other side the same way and had the same results. So both sides are now flowing oil good to the pushrods and I have oil flowing down into the head.
Apparently, even with the grooves in the rockers, there just wasn't enough oil getting through that small hole to feed the valvetrain. The old shafts I replaced them with have a bigger hole and the angled groove that allows oil to feed the bottom of the rocker. The second hole helps also, I'm sure. I don't remember where I got the older shafts from, but I'm sure glad I had them! They were in really good shape with practically no scoring at all, so I don't forsee any problems using them.
So that's where I'm at, a little behind schedule, but with more piece of mind. I'm just glad I decided to look into the head after that oil change, or I'd have never known about this issue. It's not something I even considered since all these parts were used in the past, except those HS shafts.
I'd post detailed pictures, but my phone chords are already packed and I'm a bit pressed for time. I'll try to post them later.
