Jed,
You should keep all the transmitters the same. In simulcast the main concerns will be in the overlap areas. The issues are more phase related than frequency offsets and audio deviation differences, although both of those are important as well. Most all simulcast systems are locked to a very stable time base to keep frequencies the same. The systems that I work with are GPS disciplined and the exciters are DSP based.
In the overlap areas ( area where the user can hear both or many transmitters ) phase distortion can make the area unusable. This is why it is very important in a simulcast system to carefully design the RF coverage. More power and high gain antennas mounted high are not always the best solution for simulcast. Simulcast concerns are very different between analog and digital systems.
On analog it helps to use the same service monitor to set the frequencies and deviations, but if you are using a high stability time base at the transmitters then this is not so important.
I am trying to just give some pointers. I can move to a different email if you want more in depth explanations.
The systems that I design, build and maintain consists of up to 250 high power transmitters located in the same state all simulcast.
73,
Ken, N4KCD
