I have a Sears snowblower attachment for a tractor that has a very similar setup. I would assume yours injested something other than snow, and it's now bent and banging around in the housing? That happened to me once the first winter I owned mine.
Anyway, I agree with Basementgeek that the entire auger/gearcase/axle/impeller assembly needs to be removed, and that diagram is very helpful. I'm not sure that you need to remove the entire housing (part #500), unless you can't get to some hardware.
I would start with removing the bearings (part #525) on both sides. The impeller shaft is most likely connected to the drive pulley by some screws, possibly part #481, but it's hard to tell by the drawing.
Basically, your goal will be to pull out the guts from the housing as an assembly, then remove the shear pins and any other hardware holding the augers in place. Once you find all the hardware and free the rust, this is a fairly easy job.
Remember, you want to remove the augers, axles, gearcase, impeller and impeller shaft as one large assembly. It should slide right out once you have the correct screws removed.
Hope this helps.