Lincoln ID plates are located, center front, just under the worktop.
There has been no solid consensus on what the series letters stand for;
but I have a theory that they may stood for the year of manufacture as there are no physical differences in the series types across the 2765 Models.
A, B, C, D, ... equaling 1946, 47, 48, 49, ect...
Your "D" would possibly be a 1949. I have mostly seen C's D's and G's.