I created an emonBase_rfm69pi_LPL firmware sketch specifically for the original ATtiny84-based RFM2Pi. That RFM2Pi used a different serial MUX than ATTinyCore assumes, so this firmware sketch uses SoftwareSerial. (The example I posted above uses the native ATTinyCore serial implementation.)
It is a good topic unto itself, and I have some thoughts and questions about it. So I created a topic and posted the new code.
RFM69_LPL firmware for the original RFM2Pi with ATtiny84 - Emoncms - OpenEnergyMonitor Community