I had a Ford 1700 4x4 from '82 until 2009. It is a fantastic tractor - never had a moments problem with it . Traded for current 2009 Kubota.
Your 4WD problem is definitely linkage or sheared bolt in the forward driveshaft/U joint.
Welcome to TBN and enjoy the tractor.
I just had another thought - at times that little beast can be very difficult to shift into 4WD. As you pull up on the 4WD lever, have the tractor in a very low gear(forward) and slowly let out the clutch. The lever should "POP" up and engage the 4WD. Try this same trick with the tractor in reverse. Some times I would have to do this to get it to engage properly. Remember, as you pull upward on the 4WD lever - if it does not "POP' up that last inch or so the gearing has not gone into 4WD. Hope this helps.