The ‘old’ JeeLib code is what’s now called “JeeLib Classic”. This uses a slightly different message format to Hope’s RFM69 built-in message handling code, which probably explains why you get nowt out. To add to the complication, the RFM69 can also encrypt and decrypt on-chip, which is probably impossible (memory constraints, but I’d like to prove it one day) in most of out emonTx/emonTH legacy sketches.
It should be very simple to take my JeeLib-compatible transmit-only library to send with the LPL message format and r.f. parameters, but it wouldn’t do encryption, acknowledgements or transmitter power control.
It might help to look at the release post for the CM version of the emonPi
I’m committed for the next two days, I should be able to give you a bit more time later in the week.