> command radios were designed to run on short antennas

The ARC-5 transmitter's short antenna design can be handy in certain situations, such the time I was in a temporary location and strung a relatively short wire out the window to a nearby tree.  With a chassis connection to the household ground it worked well.  I'm sure some Novices did the same back in the day. 

If I intend to drive a 50 ohm resistive load, I added a series capacitor on the output (transmitting type usually, but I have also used a heavy-duty, high-voltage ceramic disk capacitor).  Then the rig thinks it is still looking into a capacitive load and transfers power efficiently.  I believe the rotary inductor ends up close to the bottom of its travel.

On the rig under discussion, since it already had been modified with an SO-239 on the front, I installed the series capacitor inside, behind the front panel, in the line running to the center of the coaxial jack.  I think the value was 50 pF.