for 1200' I'd take discriminator audio from the RX and convert it to balanced audio with a transformer or a couple op-amps and send the balanced audio on a pair of cat-5m. power for the RX can be sent back on the other 3 pairs, I'd send 24 or 48V and have a 12V regulator at the other end.
COS can be recovered by the squelch circuit in the TX radio or with a seperate squelch board.
