I have decided to go ahead with my Open Servo Motor mount project! I just need to adapt my current motor mount designs to the larger motor and add mounting holes for an Open Servo board for motor control. This will essentially be a continuous rotation servo without the case, and any gearing down would be external.
I just need to Open Servo boards that can handle at least 25 amps of current maximum at stall, since some of the motors I want to use are R/C card/truck 540/550 size motors. I hope I am not underestimating the current draw on the 550 size motors.
With all the capabilities of the Open Servos, including built-in shaft encoders, this should be a perfect application. I just need Open Servo boards modified to handle the maximum stall current I can expect from these motors, which I am looking for specifications on now.
All the brackets I make will be Servo Erector Set compatible. 
This project will be targeted specifically at wheeled robot designs, and should not confiict with any other projects currently under way.
8-Dale