The design origin of the Pippin Spacex Surveyor 2 vehicle comes in two parts. The first is a cover illustration of Analog magazine by John Schoenherr, published in October 1962 in the US, again found long ago on Fabio Femino's extensive Retrofuture site.* Inside the magazine, there's actually a short item about the Moon Crawler on the cover, explaining its utility and the rationale behind its wide, foam-rubber wheels.
The same illustration was next used for the cover of the UK edition of Analog (looking slightly simpler in execution), and then found its way into the Man on the Moon book by John Raymond, published 1963 in the US and a year later in Britain.
Since Man on the Moon also includes an illustration on which the Molab toy (qv) was based, it's probable that this is where the Project Sword team at Century 21 found it. And used it as the base for -their- Moon Crawler, which appeared in a story in the Project Sword annual of 1968.
We don't know who painted the main illustration, but here we have the vehicle that would become the Spacex toy. Except for the wheels, where the toy appears to have retained Schoenherr's foam wheels instead of the whitewalls of the Sword Crawler, and the arms which fold on the toy instead of telescoping. In the following comic strip drawn by Malcolm Stokes, the Crawler does play a part.
The Moon Crawler in the Project Sword annual, published 1968, (above)
by an unknown painter and by Malcolm Stokes in the comic strip.
Whether planned or not, the Moon Crawler sadly didn't make it as a Project Sword toy. A small version of it (with added large antennas) was later offered in Japan by Imai and reissued by Aoshima, included in various moon base kits either tying in with their Thunderbirds or UFO-inspired series. Mike Burrows built an Aoshima base, and painted up the little Crawler in its proper Sword colours.