Matchbox 16c; Scammell Snow-Plough

The Scammell (Highwayman?) Snowplough was produced from 1963 to 1969. It is always grey with an orange tipper body and the plough has either a red & white or orange & white striped transfer. Grey plastic wheels are the preferred version, it is also found with black plastic wheels, with or without a hole in the base, no idea why and cannot find any explanation. These holes are often about getting castings off the dies but it does not seem to be the case here. One other variation is that some have the steps up to the cab pierced right through the casting and sometimes they are blanked off.