While we are on the subject of Ant's and the model which never made it into the toy line, here are a couple of examples of custom attempts to bring the toy to life. The first one is a mock up box, made with artwork from the 'Wee Willie Winkie' strip in Ranger comic.
The illustrations were clearly based on the published photographs of the Grumman concept vehicle itself.
A long while back, while bemoaning the fact that no actual toy existed, I set about cobbling together a couple of models from plastic gumball capsules. The black and white version used one of the Kinder Maxi egg capsules, which are about 3" long, Capsela wheels and and a piece of capsela Spacelink for the rear module.
The second, earlier version is a gumball capsule, with Spacex MEV wheels and a Lego brick.
The closest we can actually get to a toy version is the little space rover in the Comansi Coman Boys Space Set. The wheels are a similar sprung suspension design and the body is a nice capsule like shape.