Well, going to a simpler firmware is possible...but is in some ways a bit more complex as you won't be able to use the nice GUI tool to do it. So it's not really something I'd recommend doing unless you're fairly experienced.
So it sounds like you're able to flash the firmware successfully at this point? And you're using a 3.3v FTDI cable to do so (if you've been using a 5v cable you probably fried your RF unit on the board which could explain not being able to bind.)
You have to hook both the TX and then the RX up with the cable to flash them - but once you've flashed them the RX is setup over RF with only the TX physically connected to the computer. In your case you'd have to flash the version designed for using a RX as a TX for your "tx" module.
As for binding I found it a little confusing but by default the RX goes into bind without a bind plug or anything so it's not that difficult...just the instructions on binding are a bit confusing due to the extra stuff openLRS can support. But it's mostly like any other setup where you hold down the bind button while turning on your TX then when it beeps you let go - then power up the RX which will go into bind mode and they should link as long as they're both running the same version of the firmware.
I don't know what a GUI tool is, but I use Aduino to flash them. I use 3.3, but if all fails, then it is possible I used 5V, which answers the question!
Did you mean to say "with only the TX physically connected to your computer"?
I think they are binding ok, with the same version of the firmware with relevant part commented out. On the TX I'm talking about there is no bind button, 'A link across signal to GND on CH3 is used instead.
So it look as though I used 5V in the past sometime
Thanks Camerart.