No, this isn't an M registration vehicle. The 'M' for the registration year was at the end of the number (e.g. 'URX 465M'). The tractor shown in the photograph would have been registered before 1963.
From the page on Suffix Registrations, linked from the article you cited,
"Prior to 1963, registration marks were dateless".
We can, however, narrow the date at which the tractor was registered a little.
From the Wikipedia page on Vehicle registration plates of the United Kingdom we see that:
The first series of number plates was issued in 1903 and ran until 1932, consisting of a one- or two-letter code followed by a sequence number from 1 to 9999.
and that
By 1932, the available codes were running out, and an extended scheme was introduced. This scheme placed a serial letter before the code, and had the sequence number run only to 999, thus restricting the number of characters in a registration to six.
So it appears that the tractor in the picture was registered between 1932 and 1962.
It may be possible to narrow the date still further if you have an idea of where the tractor might have been registered (indicated by WV in this case), but as the Wikipedia article makes clear, this can often be a non-trivial task as subsequent codes
"... were allocated on a first come first served basis."
For Wiltshire, it looks like the early registers of vehicle registrations are held by the Wiltshire and Swindon History Centre, who have a blog article titled Early Motor Vehicle Registration in Wiltshire on their website which you might find of interest.
