If it were me, in this set up I'd wouldn't use the RTCM's.

I would put a PC at each site.

Configured with two nodes on each. One for the receiver, and one for the transmitter.

Using a URI or RIM for the transmitter and a simple USB sound fob for the receiver.

This lets you connect them in any way you want.

And a URI is a lot cheaper than an RTCM.

The PC's don't have to be all that expensive.

The P4's that I'm using on five of my nodes I bought on EBAY for $75 each (with shipping).

Wanna vote receivers, but not simulcast? Try XIPAR.

In fact, we're doing sort of the same thing with a split site 10m repeater.