Apparently the main issue is that the rdv4 has all of the tuning circuitry on the antenna boards, allowing for very weird designs, whereas previous versions of the Proxmark 3 have on board fixed tuning circuitry that means that rdv4 antennas aren’t compatible.
See here for a better explanation:
Here is someone else who tried what you’re proposing without modification:
(my understanding of antenna design would suggest that if you could figure out / measure the value of the tuning caps on your easy, you might be able to counteract them with other passives, but working out what works best could be very difficult) - you can see a test board by the designer of the ProxLF with multiple values for tuning here: