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I'm pretty sure those are original Holiday Buggy wheels and tires. When I got my Sand Scorcher roller it had those wheels/tires so I looked them up.
http://www.tamiya101.com/model_info.asp?id=23

I got the Holiday Buggy wheels/tires on a Sand Scorcher which uses the same wheels/tires as the grasshopper so I would think the Grasshopper wheels would work on your Holiday Buggy.

I love the name!