The NV3500 is a good trans for the 250 engine. They are not made for a higher torque installation but the 250 would be a great combination with the NV3500. I'm using a Getrag 5 speed from a 1992 GMC with a 350 engine behind my built up 292 with around 350 ft. lbs. and 350 H.P. in a 1932 Chevrolet pickup. The Getrag is stronger than the NV3500 but not quite as strong as the NV4500.