The larger the converter, the lower the stall range, smaller goes higher. Stall is dependent on a variety of things changed in the converter as well as the torque put to it. Too small with too much torque will stall too high. Too large with not enough torque may be made to stall enough but will not be efficient. I would say a 9" with 5200 to 5500 stall(on the transbrake) would work for yours. It would be tough to get an 8" to stall low enough.