The bumper is for a Mk 1 Ford Cortina, produced in millions in the early 60's. Chunky Chapman wanted a cheap supplier, so used the bumper, just like the front bumper is off a Ford Anglia 105E. He didn't care about the extra holes, which are needed for the number plate on a Cortina, he just wanted cheap chrome bumpers in around 5,000-10,000 units, which could be made to fit on the sports car profile, and didn't weigh too much.
Either plug them with black rubber grommets, or put chrome bolts on the holes.