Chuck,

Thanks for the message.   My 77 is from early 1950.  I'm attaching a photo of that hole.  It is just below the tip of my gray sharpie pen.   The gear is the camshaft gear.   The oil tube is about 5 gear teeth over to the right.  It looks like a dowel but has an oil hole in the bottom, toward the gear.   

However......   I think I determined yesterday that the threaded hole is not causing any oil pressure issues.   I looked into it with a small flashlight and saw what looked like a vertical rod.  Not easy to see.  But I found that it's a valve push rod, because when I get the pressure off that rocker arm and turn the rod with my fingers, at the top, I can see through the threaded hole that the rod is turning.

The spaces around the rods are open to the crankcase and upper value area, of course.  So there can't be any oil pressure issue with that threaded hole.

One thing I have left to try is another oil pump.  In my overhaul 2 years ago I had to replace the pump because the engine shop broke off the mount bracket.  I got a used one, from Larry Harsin I think.  It looked about like my old one.  But that is when I started having oil pressure problems.

Any suggest about where to try for a used pump?  I'm afraid new ones cost about $700, if they are available.

Anyway, thanks very much for your ideas on this.

Tom