63 Dodge Dart newcomer questions/advice

Get a measurement of how long it should be.
It just occurred to me that I pulled it out of a '64 Dart station wagon.
The Dart wagon is on the Valiant's shorter wheelbase (106" vs. Sedan/Coupe/Convertible's 111") - I suspect the driveshaft length may be different, but don't know for sure.

Yes the DART station wagon has a drive shaft that is the same length as a valiant. Both the Valiant wagons and the Dart wagons were built on the same platform. Therefore, your Drive Shaft won't work for him if he has a Dart. I do have a drive shaft for a Dart that is a slip joint made to replace a ball and trunnion drive shaft. It's still bolts on the front to the transmission, but has a slip joint. Too bad you're on the other side of the country.