So to add to what I put earlier and add to Nigel and truck shop have intimated at
The A30C is a very solid and robust truck, so much so that we don't tend to sell half of much parts wise for these old girls compared to the A25C 's of the same age, with that though comes the caveat, when something does go wrong it goes WRONG.
These trucks are primarily 6x4 ( front two axles ) that you then make 6x6 with the longitudinal diff lock, then you can lock the front diff only in 6x4 or 6x6, then the final "oh schit i'm really stuck" is the button on the floor to lock everything, so to remove the front prop something has probably gone quite wrong as they have removed drive to a pair of the primary wheels, personally I'd be checking the front diff then the planetary caps to make sure all the components are there, I don't think the drop box is an issue as you obviously have drive to the rear axles, OR everything could be ok and someone just wanted the front propshaft maybe.