i know this is a old post but for future readers to use a np203 with a 700r4 you will have to swap out the tailshaft out of your th350 into a 700r4, they have different spline count tailshafts. there was a place i found that had different splined tailshafts for 700r4's you could buy for conversions like this but i cant remeber where. if i find it ill post!!