1: Luggage rack fitment is dependent on the manufacture of the sissy bar. there is no standard, so they range in widths, lengths, bolt spacing etc.
2: Drilling out your new luggage rack to make it fit is a BAD idea as the steel used below the chrome plating is VERY poor and rusts quickly
3: You get what you pay for. I had a similar Flea-Bay luggage rack for a while on my C50. Not only did the chrome flake off and the underlying steel rusted in under two years, but the welds broke from the pressure of mounting my topcase to it in place of the sissy bar.
4: Luggage racks have a MAXIMUM weight capacity of only 11-20 pounds. Overloading them is easy to do and they WILL fail after prolonged use if overloaded. If you are planning on actually USING the luggage rack, I would suggest getting much sturdier such as the Wompus Bike Rack
Wompus Bike Racks - Home of Heavy Duty Custom Built Steel Motorcycle Racks
No, they aren't pretty, nor are they inexpensive but they're sturdy and will not fall apart like the cheap Flea-Bay edition.