Just thought of something. What year is the engine this trans is behind? I ask because 67 and earlier engines had a small crank register and 68 and later have the large register. You can use a 67 or older trans behind a 68 or newer engine but you need an adapter to properly center the torque converter in the back of the crankshaft. If you don't use the adapter it can possibly break the input shaft on the trans. and/or damage the pump and converter. If the engine is 67 or older you can't use a 68 or newer trans. behind it without a specially built converter.
