If you're referring to 6U7314, that would be a 1952.
Lets see your tractor please. Some of us grew up on those things in the orchards. Around here in N. California, seems as if everyone owned either a D2 or D4 tailseat tractor whether it be for their prune, peach or nut tree orchards. Ours was D47U7901 and was eventually traded off to TENCO or Holt as a parts machine to help offset the repair costs of a Kubota 8030 we owned. That D4 was well beyond worn out, but it had a really strong engine and dependable pony. Fond memories. JM