</font><font color="blue" class="small">( difference between an overide clutch and a slip clutch )</font>
Instead of "overide" it's called "overrun," but that's only important if you are doing an internet search and need to get the exact name. The overrun clutch is really a misnomer. It should be called overrun ratchet because it works like a ratchet in one direction only. When your tractor is applying power, it locks and transmits the power to the implement. As Chim indicated, if centrifugal force causes your implement to keep running after the power is removed, the "ratchet" action allows the implement to spin down normally. Some newer tractors with independent PTOs have a braking action on the PTO to slow the implement. An overrun clutch defeats that action. The overrun clutch is about $45.
A slip clutch is a better solution if you want to have one installed. I'm not sure of the price, but I think they are more than the overrun clutch. It replaces the shear pin's action. I'm pretty sure you have a shear pin on your snow blower. Look at where the U-joint attaches to the snow blower. Does it have a bolt through the U-joint collar? If it does, that is the shear bolt. If you hit a rock, that bolt will snap off and you will have to replace it with a new #2 grade soft bolt of similar size.
Finally, the PTO extension is available from many farm/tractor dealers, and Ken Sweet might also have these. They come in various lengths, but I don't think I've seen one less than +6". That might be too long for your application. If you can make the modifications Ken suggested, you might be better off. Adjustments like that are common between tractor models and is sometimes referred to as "setup" by tractor dealers.
Good luck getting the correct "setup" for your snow blower. /forums/images/graemlins/cool.gif