In 1973 Chevrolet was required to increase the crash resistance of the bumpers on its vehicles. This began the era of the "big bumper" Novas. In order to be able to accommodate an up to 5 mph impact, the bumpers were pushed out away from the body 2-3 inches which made the bumpers look really bulky.
Big Bumper Nova owners wishing to clean-up the look of their 73-74 Novas have two choices. They can swap the nose trim, grill and bumper for a 69-72 setup which is a basically bolt on swap as the fenders are the same, but this is not cheap swap and it changes the personality of the 73 nose. The alternative is to perform the "bumper tuck". This is fairly quick and cheap.
On the front and rear, the bumper tuck eliminates the 2" plastic/vinyl trim that is suspended between the bumper and the grill or end panel and moves the bumper back to sit abutted to the grill or rear panel. On our car the rear bumper tuck was performed by the previous owner (who told us he also replaced the rear bumper with a 1974 bumper).
Since I had the front grill removed for paint, I decided to reassemble the front end with a front bumper tuck. Step one was to notch the bumper bracket. These bolt to the frame and when you slide them back without the notch they will run into the radiator support.
After several tries and test fitting, this is the final cut I used. 4-1/2" from the rear edge and 4-1/2" wide. (You can follow the slope of the detent in the brace in for the last 1-1/2".)
Next Drill the new holes in the frame with a 1/4" or 5/16" bit and then finish the hole with a 1/2" or 9/16" drill bit. I only had a 1/2" so I needed to the clearance the holes so the bolts would slip through. The brace is now bolted to the frame using the first two bolt holes on the brace.
Lower Bumper Tuck Alternative
I also wanted to see how it looked if I bolted the bumper below the lower grill and headlight trim. The upside is you can move the bumper further back about 1/2", the downside is the 2" gap between the bumper and filler panel that would need to be filled.
To do this I added another elongated hole lower on the frame rail. (This pic is before I connected the two holes.) For the back bolt I used the existing slot in the frame.
I'm thinking a Spoiler by Randy might be a good addition to the front...