If it was correct then the first digit behind the model would have been a "G" for gas. With a "D" (standing for diesel) tells me you have a rearend switch at sometime in its life.
The serial number codes are:
Model number (44, 22, etc)
Engine type (B-butane, G-gas, D-diesel, etc)
Altitude (1-regular, 5 hi altitude)
Style (R-row crop, S-standard, V-vineyard, etc)
Clutch (F-foot, H-hand)
Hope this helps a little.