Whoops. Gonna hafta suspend that merit badge.

Actually I have nothing to contribute here except a bump. I know not nothing nohow about a 740's radio or heater, but your post was getting pretty lonely at the bottom of the brickboard.

You could always verify continuity through to the antenna. The way I do it, or did it some 40 years ago when last needed, is to connect the ohmmeter to the sleeve and tip of the connector going to the radio and then using a jumper wire to short the antenna to ground (or the connector at the base of the antenna). It is fine wire, so don't expect zero ohms, but there should be something!

BTw it was an interesting read about the manipulations one needs with a 7mm nutdriver. I envision those flexible long-shank nutdrivers employed by TV repairmen (ususally 1/4") in the 60's as a better approach vs. a bunch of 1/4" drive extensions to mechanic's ratchets and sockets.
--
Art Benstein near Baltimore

Marriage is a wonderful institution, once you are ready to be institutionalized. - R. Cooke