Some of the older units did not have a seperate scraper blade on the bottom edge. They just used the edge of the housing. I'd say the bottom edge of yours is plum wore out. If you can get a bottom scraper blade, then install it on your machine. Evidently you will have to drill matching holes. And, if your drill bit doesn't want to penetrate the metal, then go to hardware store and buy 1 or 2 of those gold colored drill bits, for tempered steel,
and go to it! Mark the holes and drill away. Get the size for the bolts you are going to use. And use lock washers when assembling it.
NOTE: With using the bottom edge of the auger cover for a scraper, you may have to get somebody to weld on a section, so the separate blade can reach the ground.

friend bought similar used unit last fall. the impeller section separated from motor section. unit basically collapsed. i think his welds broke. so it bolted it back together and it works ok now. i mentioned my unit was similar and looked closely and i do have a series of perimeter bolts in the impeller section. maybe i really do have bolts where my blade bolts on? its all iced up today after blowing wet snow yesterday. there is a blade scraper that appears to be welded to the bottom of the auger section. will have to inspect it more closely.

yes there is a bolt on blade. seems to be worn. adding or modding a replacement seems logical. would a new blower allow the blade to come in contact with pavement? a stock replacement blade might get close but a modded longer blade can be any length you choose.