I had an EICO FET TVM. I still have it. D Cell for the ohmeter and a 9V battery for the voltmeter.

Mine had the phone plug as yours does and also. The probe was quite large in diameter and could turn to insert/remove the resistor (whatever value it was).

I think it was AC/Ohms and DC,

I doubt the cabeling matters and RG-58 would probably suffice.

If you keep your voltages down, RG174 is about 1/2 the diameter (0.1") of RG-58

RG58/59; http://www.scp-sa.es/resources/uploa.../RG58_RG59.pdf

RG59 is TV stuff with a solid core.

RG174 https://www.awcwire.com/productspec....-coaxial-cable is good for 1500 VRMS and it quite flexible.

If had to actually make a probe and it made a difference as to whether the resistor is in the tip or the plug, You can get a BNC for the probe end.

But then some of the standard probes could likely easily accommodate a series resistor inside. Especially some of the adjustable probes like these: https://www.fluke.com/en-us/product/...ads/fluke-tl40