Mine has no bracket -- just holes in the boot lid for the upper license plate bolts:
I made some rubber washers to protect the paint there.
I'm confident that these holes are original as the car has original paint and those nuts had the same funky grey plasticene on them that were on the other bolts and speed-nuts and that a former TR employee assured me was the original goo.
I would be concerned that that bracket would not stand up to the weight you will put on the luggage rack with a suitcase or such.
Nervous work drilling in fine paint. The guy who did my TR3A thoughtfully welded up the holes for the rear 'TRIUMPH' badge and I got to measure and drill the replacement holes.
Sorry, I am away from home and cannot give you exact locations of the holes on mine.
PS - With that bracket standing proud of the surface of the boot lid I'm not sure the luggage rack would even mate up with it properly -- I'm thinking the rack 'legs' want to be mounted against the surface of the boot lid.