Ray, I cannot answer for the older Cubs but on my 782 That is true. When engine is cranking the Key switch disconnects Regulator. The schematic for the 782 shows this disconnect. When I made my own harness, I deleted the Keyswitch all together and put in a Push button switch to the Starter. I added a relay that disconnects my regulator to the battery during cranking just to keep it as it was electrically. Not sure if what the old '30's cars disconnected the regulator when they had their push button Starter setups.
I guess is would burden the Cranking process to try and charge the battery hard as it sees a voltage drop when the Starter is cranking.
Dennis, I'm so glad you mentioned that. A friend bought a 123 from me, he just mows with it, and it eats head gaskets. Overheating is evident and I've mentioned to, not told, him that he should run WOT and gauge his speed with the hydro. I guess I gotta get a bit more aggressive, huh?
Yup, I know I'm just "giddy" as hell playing with my 45+ year old tractor and it isn't even working. Plowed out the 5.5 inches wi no problem at all. Still snowing pretty good, maybe head out again in a few hours and do some night time snow throwing.
Watching The Winter Classic, and I think that what is coming your way.