I don’t think you need a bracket to mount that blower on that tractor. Do you have a large pin sticking out on the front of each side of the frame? The notches on the blower should fit over these pins. If I’m wrong post back with pictures of the sides of the frame and model numbers of both the tractor and blower.
Go to Sears Parts Direct with this model number, 486248463. There you will be able to download a manual for your blower. Then you will be able to figure out which parts you are missing and what you will need to order. You are correct, either someone removed parts or you purchased the tractor and blower separately, not getting all the blower parts.
