Chain drive is supposed to give you a better transfer of power throughout the driveline because of the driven contact area on the gears/chains/sprockets. J.I. Case used chain driven rear ends well into the hundred series tractors. I think the Case 730 was chain driven if I remember correctly.
Good day My former employer had Case D & when u were at a place were tractor was going to free wheel, you could feel something was not driving or holding you back, probably slop in drive chain. Thanks