You will probably need to have a C4 Yoke, I don't remember if the Ford O Matic Yoke is the same spline right now been a long time since I seen one of the Ford O's, but another site member will probably know that answer. Being that you have the Ford O try that Yoke out first to see if it goes in easy into the splines. The driveshaft length should be about the same for both the bad thing is if the C4 Yoke is needed you will need to get it adapted to the driveshaft or get a different one I.E. the front U Joint Yoke of the Driveshaft is a different wider size. It might be cheaper and or easier to look for a 1965 Falcon C4 Auto Trans Driveshaft that should fit right in place. For your driveshaft length you will need a minimum of 3/4 inch clearance from the front of the Yoke to the back of the tail housing for the yoke to be able to slide in during the rear suspensions movement and not cause any trouble driving about the max that the Yoke can be out is 1 1/2 inches more than that and the drive shaft is too short, 1 inch out is about perfect.