Thanks John. And as for keepng it, well, I wouldn't part with it for most anything. Me and my tractor been through alot. Just something about dragging your elbows in the dirt that you can't get on a larger machine.
Go to "www.tractortips.com". Click on "specs and serial numbers", then follow the instructions.
According to that site, your "D" model was indeed made in 1978, as John Miller suggested. However, it appears that if you have the "DT" model instead, those were not produced until 1980. Don't know how accurate this info is.
Well, kubmech, it seems that the n..'s are slightly different in size, with the right one being larger, for the most part. If I had to give one away, I'd choose the smaller one. Just a thought.