Yeah, that was a fumble with the frequency. You could measure the inductance of your proxmark antennas with a $40 LCR meter, and if they happen to be 203μH (the inductance of the ProxLF) then you could just drop it in. I highly doubt they’ll match though. Every little bit off of the target inductance value will dramatically affect tuning of the resonant circuit created. You can check out more about it here, if you’re interested.