I have been playing around with a calculator with two restrictions in mind - 170 Hz shift per channel and Total bandwidth  of 850 Hz.

I would like to propose these audio frequencies;

Channel 1 - Space 2295 Hz

                 Mark   2125 Hz

                 Shift    170 Hz

Guard band 510 Hz

Channel 2 -  Space 1615 Hz             

                  Mark   1445 Hz

                  Shift      170 Hz

Total bandwidth    -    850 Hz

Channel  1 -  is obvious  Standard TUs will work with it

Channel 2  -  a Dovetron should be tunable to 1445-1615 both send and receive

The two channels could carry the same data or different data.

Tom   N3CRK