The HRO tuning mechanism is a right angle gear drive with a 0 to 500 counter
built in to the knob and you can spin it,

Tnx JFR for the additiona and clarification.

Did the HRO have two or three stages of RF?

I has very little backlash because of pre-loaded gears

I seem to recall that all military comm gear of that period had those kinds of
gears. Each gear was a pair or "split" with a shared spring. The tension on the
gear teeth was obtained by rotating the gears in opposite directions and then
meshing them with the connecting gear or worm.

A popular military receiver was the BC-348 and BC-342. I forget which, but one
operated on 14 or 28 vdc and the other on 115 vac. The dc unit was easily
converted to ac.

Another colleague, a strictly CW operator, used one of those to rack up lots of
DX. That RX and a Meissner Signal Shifter feeding a war surplus 304TH was a
powerful and inexpensive CW station.

73,
Bill, K5BY