Success !!
Frank, your suggestion the motor was on only one cylinder was correct!- the lower had no spark
I tore into everything at the lake yesterday, and found I have the early 1951 style coils which looked amazing, and the Stevens tester confirmed they put out a hefty spark at 1.2 amps
I cleaned the points and installed some .75 cent capacitors (.22uf) from Digi-Key in the place of the old condensers
As simple as that was, I was previously in denial the ignition could be at fault.
May this be the last time I don’t scrutinize the ignition first!
Now the motor runs at full, planes the boat with two people……
And I learned a bit more about 2-stroke carburetors!
Thanks to everyone on here who has been so generous with their information, experience and time.