Welcome to the forums, Tim
I am going to be a pedantic jerk and clarify/correct your reference to "advance design".
AD = A-D = Advance-Design: 1947 to 1955 first-series Chevrolet trucks
and
ND = New Design: 1947 to 1955 GMC trucks (GMC did not used the official designation of 1955 "first series' to distinguish the 1955 ND trucks from the late 1955 Blue Chip GMC truck body style)
I am not certain if A-D and ND series names were used in both countries, but I would guess so (same goes for the later series names of Task Force Chevrolet and Blue Chip GMC)?
Canadian GMC trucks seem to sometimes have subtle and substantial differences in comparison to same-year GMC trucks made in the USA. You'll find there are differences in the engines used in light/medium duty 47-55 USA & Canadian GMC trucks.
Of course, Bill's answer is correct regarding wipers. Most likely you are referring to a 1951 truck. There is one style of A-D Chevrolet truck, 1954/55, where the after-market electric wipers might not install properly with the accessory radio (the 54/55 GMC truck does not have this "problem").
Most likely this post contains too much information - sorry. However, here is one more piece of advice: your name gives away that you are probably referring to a 1951 GMC. You might want refer to your brand/year/model in your posts (and perhaps in the "signature" in your profile - click on the "My Stuff" link above and then click "Edit Profile").
