Thanks fellas. Looks like I'll have to save my pocket money for a little longer! I'm probably better off finding a decent set of used wheels anyway, as I still use my Special as my regular mower.
On a side note, I don't suppose anyone could hazard a guess as to when a Model 5 with a serial number of 289283 would have been made, and what type of snorkel (short or long) it should have?