This is a nice model and is one I had when a kid. It took me a long time to realise that it was a very small scale model of an enormous piece of road building machinery.
The Allis-Chalmers Earth Scraper, K-6/1, was released in 1961 and remained in the range until 1967. It is in a number of shades of orange and has either silver metal or red plastic hubs. There is no really rare version, red hubs are marginally less desirable, but only marginally according to the price guides. However I've had lots of the silver wheel version through Little Wheels, but I've never had a red wheels one - which seems to suggest it is rarer.
