The C300Y40 was a cheaply made copy of an older Clark model CY40. Most of the parts, except for the engine, are hard to come by for this truck. I would not recommend it at all. The C500Y40 was a great truck for Clark with excellent parts availability. As a matter of fact a lot of Clark people like it better than anything they've come out with since.
The HY stands for hydrotork transmission which is a 2 speed automatic.