Tranmission lines are different. The torque converter from the truck has very little stall. If you get a replacement converter for the 340 it will have a better stall that you won't notice under daily driving. It will also be balanced for your motor. It should be the converter with the large ring gear. The small 904 flex plate will bolt right up to it. This is for your motor stock. When you build it you may want a higher stall than factory. You will need a converter balanced to your crank cast, or steel. You will need a shorter drive shaft with the 727 tranmission yoke on it. There are two U joint sizes. If you buy a used shaft make sure it fits the rear end yoke on your car.