What size rear tires?
With 6"(13"), and a 700, we used an 8"to 5", then a 15 trans. The rear we had in 2 tooth increments from 42-56
With 8" (16"), we used a 12 on the trans. All else remained the same.
90' straight, we would probably have a 52 or 54 on it, and spin it about 6500.