Hi Jay, I have two 450 blowers. The 450/451 blowers are not designed for the QL's and older models. They use a larger "B" section v-belt and the QL's and older use an "A" section belt.
I did purchase my second blower from someone that converted it over to work on their 1650. They changed the idler sheaves and cut out a new pair of lift links and welded a piece of steel to the top of the lift shaft and bracket on the blower to use the pull to lift function The side panel on the right side had to be removed otherwise the lift rod would damage the side cover. I did bolt it up to my 1650 and was going to use it in the snow but had trouble with keeping the "A" v-belt on while lifting and lowering the blower. The blower also would not float on the ground. Basically down was as low as it would go and if you encountered a dip it would not drop to compensate for the dip.
Since he gave me everything to change it back over; in the spring that is what I did. I ground off the piece that was added on for the lift and changed the larger idler sheaves back over to the factory lift links and will use it on another 82 series sometime. I give the guy credit for the attempt and that he didn't hack it up to make it work.
I do see from the parts look up under 1650 attachments they did make a 364 two stage blower that will work. An IH design and probably a CCC design. I think these might be a little hard to find. They also list Haban single stage throwers. I'd like to get one to compare to the QA's. I've seen a few for sale in my area but they were missing parts.
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I believe the 451 is the same as the 450 with the exception of the gear box like Ipalma said. The 450 is designed for the tractors with a 4.5" diameter electric clutch sheave. The 451 is designed to be used with later model tractors with the 6" diameter electric clutch sheave. The gear box on the 451 has a slower gear ratio to compensate for the difference in speed and torque from the larger 6" diameter sheave.