If my memory serves me correctly NAMBA is more flexible as far as the course radius goes. So, I would just run a 1/3 mile IMPBA course which has a radius of 35 feet and a straight-away of 330 feet. Six laps of racing gives you a mile long course.
The above course is 1/6 mile. 6 laps = 1mile. I found the above course in both rule books. Namba's is in the elec. section.. 35ft radius turns 330 ft straights.