I have a 1971 D300 dually with a 4 speed trans. I believe it to be a NP 435. However, when trying to order a kt to install a GearVendor overdrive i have from a later Dodge with a 5 speed, the guys at GearVendor wanted to know which 435 I have. They told me to measure the distance between the two top bolts and two lower bolts at the rear of the tran. Apparently on one NP435 used has the measurement the same, top and bottom . On another NP , which I have. the bottom bolts are further apart than the top pair. So what can you add to this??? Thanks R