> I have also buzzed out each line from plug to PCB, and all is good there.

Did you "buzz" between the wires to see if any were shorted?

> However, when I open Chirp and try to download the radio, neither of the two led's associated with TXD and RXD lights up.

Still sounds like there is a programming cable issue.

> Although this is a UV-5R Plus, do I still use the UV-5R option, or should I be using the BF-F8HP as the model?

UV-5R: radios with 2 power levels (HIGH/LOW)
BF-F8HP: radios with 2 power levels (HIGH/MID/LOW)

> Oh well, plan B it is then - get 3 wires and one each of 3.5mm and 2.5mm stereo jacks!

This is what I did.

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