I don't claim to have this all figured out but I think your backing plate and drum need to match your axle bearing to flange (where the wheel bolts up) offset. I think the offset is narrower on the small bolt pattern(4") and wider on the big bolt pattern (4.5"). You can buy aftermarket big bolt pattern (4.5") axles with with the narrow offset so you will need to measure. Hope this helps and if this is incorrect someone please correct it.