I misread the OP, and thought it was about using an existing RG-8X cable (50 Ohm) for a TV application which is 75-ohm.
I now see that it is for a VHF radio, which of course works with a 50-ohm coax, and not the 75-ohm cable.
An intermittent connection may not be good for a transmitter, as the latter needs to see a constant load. So, whatever you do, make sure you have a good connection. And jury rigging may not be advisable anymore.
"Old age is the most unexpected of all things that can happen to a man" -- Leo Tolstoy