Hi Mike
I just joined... and don't want to step on any toes... but I've been running Chev 6's doing the for jobs they were designed for, for a lot of years. And I've driven them flat out and fully loaded with splash oiled 2 tons and pressure oiled 3 tons. In all those years I've never worn one out to the point of needing an overhaul.

Having said that... the old splash oilers were designed to use Nothing Heavier than SAE 20 at the hot end until ambient temperatures were over 90 degrees... and we never did. Anything heavier than 10w-30 is way to heavy to spray out of the oil nozzles and hit the rod dippers the way it is supposed to.

Tolerances in the old splash oilers were actually Tighter than the pressure jobs. Rods for example run as close as .0005", and should never be more than .0015" clearance. Check the factory specs if you don't believe me.

Now as to your oil pressure problem... with cold oil, even with something like a 5w-20, you should be seeing something around at least 20 pounds at start up, and about 14 pounds warmed up and around 2000 rpm.

If you don't, and you have oil at the top end as your video suggests, then the first place I'd look is at the metering valve on the left side of the block. Due to the design, splash oilers Will Not develop oil pressure unless the metering valve is working. In fact, the sole purpose of the metering valve was to develop pressure to show on the gauge, and pressurize the mains and cam bearings 1935 and after, and metered pressure to the rocker arm shaft 1940 and later. All main and cam bearings were pressurized by 1932, and the rods oiled by pressure stream 1935 and after, with the top end oiled with metered pressure by 1940.

The supply to the rods runs under essentially 0 pressure flow from the down stream side of the metering valve and has no bearing on the pressure registered on the gauge at all.

Check for a bad spring or the valve stuck open. Also check for the right gaskets on the right sides of the valve. The inner and outer gasket are not the same.

And the metering valve is the easiest thing to get at too!

Interestingly, the 1929 engine ran 0 pressure to any part of the engine. The metering valve did nothing but develop enough pressure to show on the gauge so the driver knew the pump was working.
Good luck! Hope you find the problem!
Ole