Well call me crazy, I bought on EBAY, a data plate for a D4 7U 20668, which I do not own.
I would enjoy keeping this with my collection of things but think I should at least try and find the tractor it actually was attached to so who ever might own it could enjoy it.
It appears to be cast brass or bronze and has more info than simply the tractor S/N as you should be able to see.
If my search is not productive I will enjoy it.
[attachment=30265]D4 7U 20668 data plate.jpg[/attachment]