The brackets you're showing are 72 and earlier. Y brackets are correct for 73.
Personally, I wouldn't bother with the L bracket.
Replacement fenders are drilled after fitment to match bumpers IIRC. Factory fenders, I'm not sure. You may have to redrill your fenders. If so, be very careful to place hole so that the sides are 90 degrees horizontal.
You may be lucky and the old fender holes line up with loose adjustment of the bumper or they are covered by the large rubber washers. If they are exposed you could fill the holes with stove/carriage bolts, painted or ss OR repaint the lower fenders after filling the holes.Good luck.