Is this factory? 1974 fixed bumperbumper
The '75 frame rails won't have the mounting points for the non-shock mount brackets, that will be the toughest part.
It's not just holes either, there are nuts inside the frame that are welded in. So, to mount the standard brackets on a car that doesn't have the standard bracket mounts you'll either need to open up the end of the frame rail and weld the captured nuts into the frame rail, or drill completely through the frame rail and use long bolts so that the bolts go completely through the rail so you can put the nuts on the other side. Problem with that last method is that you could crush the rail if you over tighten the bolts, unless you add a tube inside the rail. So if I was going to do it that way, I'd locate where the holes need to be for the brackets, drill the holes all the way through the frame rail, and then oversize the holes so that I could slide a tube through the frame rail. Then I'd weld the tube so it's flush with the outside of the rail, and then you could use the long bolts that would pass through the rails and put the nut on the other side of the rail without worrying about collapsing the rail if you over tighten the bolts, or worry about them ripping out of the frame rail in an accident. Given all of that, it might be easier to just locate the holes with the brackets, then open the end of the frame rail and weld in the captured nuts.
Also, be careful about buying the '74 bumpers. The shock mount bumpers and the standard bracket bumpers have the bracket mounting holes in different spots, so, those bumpers aren't interchangeable. So if you buy a '74 bumper the ideal thing would be to buy one that has the brackets with it as a single package, so you'd know you're getting the right one.
My '74 non-shock mount front bumper (I sold this awhile back, fyi)
Another '74 bumper. I assume this is for a shock mount, although it's a picture from eBay. It was from a '74 Duster though, and you can see the holes for the brackets are in a different spot.
The '75 frame rails won't have the mounting points for the non-shock mount brackets, that will be the toughest part.
It's not just holes either, there are nuts inside the frame that are welded in. So, to mount the standard brackets on a car that doesn't have the standard bracket mounts you'll either need to open up the end of the frame rail and weld the captured nuts into the frame rail, or drill completely through the frame rail and use long bolts so that the bolts go completely through the rail so you can put the nuts on the other side. Problem with that last method is that you could crush the rail if you over tighten the bolts, unless you add a tube inside the rail. So if I was going to do it that way, I'd locate where the holes need to be for the brackets, drill the holes all the way through the frame rail, and then oversize the holes so that I could slide a tube through the frame rail. Then I'd weld the tube so it's flush with the outside of the rail, and then you could use the long bolts that would pass through the rails and put the nut on the other side of the rail without worrying about collapsing the rail if you over tighten the bolts, or worry about them ripping out of the frame rail in an accident. Given all of that, it might be easier to just locate the holes with the brackets, then open the end of the frame rail and weld in the captured nuts.
Also, be careful about buying the '74 bumpers. The shock mount bumpers and the standard bracket bumpers have the bracket mounting holes in different spots, so, those bumpers aren't interchangeable. So if you buy a '74 bumper the ideal thing would be to buy one that has the brackets with it as a single package, so you'd know you're getting the right one.
My '74 non-shock mount front bumper (I sold this awhile back, fyi)
Another '74 bumper. I assume this is for a shock mount, although it's a picture from eBay. It was from a '74 Duster though, and you can see the holes for the brackets are in a different spot.
