rear brake and spindle are almost cirtainly smaller. The spindle issue might be got round with spacers / sleeves. Less powerful (smaller so assuming less stopping power) brake on the rear might well be a bad move, though the superdream's not far behind the 550 on weight so might be ok for actual stopping ability, you might have brake fade issues. Front wheel I think would fit but brake disk alighnment and diameter might catch you there. A cb650 rear comstar is however a good match and will slot streight in and look good in my own books at least (tried it on a 550k3 so spacers might be dfferent?)