some physical difference between WDM2,WDM3A,WDG3A.
Physical diferences between wdm2 ar wdm3a is quit same it is like impossible to determine which is wdm2 or wdm3a.only a expert can tell the apart like me.
Wdm2 both end are flat and no wdm2 made with short hood like wdm3d.Wdm2 has grilled cowcather only SPJ has a wdm2 with solid cowcather.
Whether some rebuilt wdm3a have one...
more...

end is short hood and solid cowcather like emd locos.
Difference between WDG3A in comparing to WDM2 or WDM3A is very easy.WDG3A are longer in length compare to wdm2 or wdm3a.One more difference is their bogies are different from wdm3a or wdm2.wdg3a shares it bogies with wag7 and wdm3d whether wdm2 and wdm3a shares its bogies with wag5.wdg3a comes in both grilled/solid cowcathers and short hood like wdm3d variants.