Ok, just adding a bit in here from my side:
Relay 1-3 are triggered using the existing 3904s onboard.
Relay 4 is a drived via a new 3904 and an extra digital I/O.
Firmware changes will be needed regardless as its one output on at a time per filter.
Added 100uh smd inductors for RF filtering.
If you all like it so far. I will make 10, and happy to post to a few of you with test equipment at no cost, please contact me if you want one.
73 Nick VK4PP