We used to do this to provide comms for a 3 day youth soccer tournament.
The receive site was about 2 miles (as the crow flies) from the transmit site.
Receiver was on a tower owned by the board of education (with permission), and
the transmitter was on the roof of a hospital. Both entities supported the
tournament, and they were happy to help us out with siting.
It worked pretty well.
I think your separation will also work pretty well. You are far enough apart
that the antenna for one half is not in the near field pattern of the other half.
More separation is usually better, but too much separation is not helpful.
Cautions:
1) Make absolutely sure you aren't going to interfere with existing repeaters.
Check with the link frequency registrar for your area. He is usually part of the
repeater coordinating body for your state. Since link frequencies are usually
kept confidential by the owners of a repeater with remote inputs, it's way too
easy to accidentally step on someone's remote input link. I know because this
happened to us one time. We thought we were operating using a low profile,
but we were inadvertently bringing up, and being heard by a repeater in a
county 40 miles away. Oops! Don't be THAT guy!
2) Unless you have some kind of controller operating to automatically ID your
system, the users will have to ID the system as they use it.
3) Check with your repeater coordinating body to make sure you aren't on
an existing repeater frequency. When we would setup for our event, we
used to file a temporary coordination for the pair we were using. We were
good for 2 weeks prior to the event through 2 weeks after the event. This
was to give us some leeway as to when we setup and dismantled our
temporary cross-band repeater.
Some people really seem to have a high level of disdain for their local
repeater council. Sometimes they CAN seem to be a pain in the butt. But
they're doing a job, and they are a resource for you to use. Work with them,
and they can make your life MUCH easier.
73 de N8AUC
Eric