I don't think the model 450 will exactly fit your 782. I have a 149 wideframe and I tried to hook my blade from it to my 1882. It did not fit. I can't remember for sure, but I think it was not long enough to clip into the back frame. Granted the blade isn't the same as a blower, but it did not bolt right up.
I think the 782 and the 149 can take most, if not all, the same attachments, but don't quote me on that. Maybe someone else could verify if the 782 and 149 are interchangeable with attachments?
Now my 1882 has a model 450 blower on it, so I know for sure it does fit it. Could it be made to fit your 782, maybe, with a lot of work. I went through the same exercise last year with my 149, as it has a QA36 single stage blower, and does not work well at all in the slush. My solution was to buy the 1882 and scrounge for a blower last summer. I just used it yesterday and today during the snowstorm. It worked pretty well, much better than the single stage. It is interesting to note that my brand new Ariens 8 hp walk behind, will throw the snow much father than the model 450. But it is 20 years newer and the blower designs have advanced over the course of time.
Happy New Year, Tim in Mass