SJH,
Love the pictures- nice work on the components. I did a simple DC motor conversion using a treadmill motor on a machine. Keeping the motors cool at low speed was a concern since they do not have a fan. I found a 125V AC computer style fan at Surplus center and mounted it right on the end of the motor using the motor bolts and a simple adaptor plate. I wired the fan to the 125V on-off switch that went to the DC controller. I used a double pole double throw toggle on-off-on switch on the DC out put to the motor so I could reverse it. After running the motor, I can leave the 125Volt switch in the on position so the fan keeps running while putting the DC reversing switch in the off position so the current to the motor is stopped. That way you can cool the motor down for a few minutes after you finish.