Mike,
I do not have enough knowledge to determine the best backer style, but one positive you have is the power source of 120 volt. That gives you many options as to the motor drive equipment, think back up motor that is easily changed out due to a failure.
With the abundance of 120 V motors and gearing available you will need to decide on what backer you desire.
If you go with a single direction system like Calgary, you need to gear it to be able to run for 10 minutes which requires a slow moving backer, but fast enough to pick up shoots fired a couple of seconds apart.
The other option here is to have reversing limits at both stop points to reverse the backer travell.
The risk is the delay in reversing causing a potential overlap of bullet holes on the backer paper.
The other system, as Bill and other have shown, is a faster moving backer that is in a continues motion due to the drive motor not having to stop and change direction. There is delay in this system at each end of the stroke as the drive cable goes from pulling to pushing. This delay is very minor, and seems to be favoured by some of the bigger ranges in the US.
I would think that the boys going to Kanas will be able to get good idea of there system and help you decide which method to use.
Just some thoughts on the systems I have seen.
DanO