Please refresh my memory on tranny interchange

The valiant will have a 904 unless someone put a 727 in it. Are you sure that's a 727 in the truck? I know they did that in the 70's but not sure in the 80's. They had a short and long tail 727 and if it's the short tail you may be able to just swap the 904 yoke on the driveshaft and swap trans. Pics of the truck trans? Measure your 904 from bellhousing to tail shaft and the same on that truck. IF they are the same length it may be a simple swap.