According to the Gruhn book this spec Wiltshire was made from 1963 to 1970.
I would measure the width at the nut. If it's 42/3 mm then it will be the earlier spec so that would date the guitar to 1965 or earlier. If it's 40 mm then it will be 1965 or later.
I do like the minhumbuckers.
That's great info, thanks. I shall dig out my Vernier calipers as soon as I get home!
EDIT: And the answer is....40mm so it's 1965 at the earliest. I'm tempted to say 1965 is probably the date then because of the holes for the Vibrola which, as far as I can tell from online sources (pinch of salt), was not offered after 1965. I can't imagine anyone retro-fitting a Maestro Vibrola but there are some weird people out there I guess...