And one more note - the WD had at straight gearshift up to sn 127006 in 1952. If you see a straight gearshift it's a WD. The constant-mesh transmission had a curved gearshift and was in the last WD's (sn 127007 and later) as well as all the WD45 tractors. I use the gearshift for an initial ID, then if it's curved I look at the side of the engine for the plate already mentioned - if the plate's there it's a WD, if not it's a WD45.
They were very similar tractors - the WD45 had a slightly larger engine (226 cubic inches .vs. 201 cubic inches).