Those are the right year bumpers. The holes in them and the shinier chrome lines are the remnants of the 70's 5 mph safety nubs. If your looking for ones without those, you're going to need 71-72 bumpers, but those are running such a price these days it might be cheaper to weld up your current ones or go for fiberglass ones from toysport. Of course if you're not as OCD as me, you can just leave them and they'll look pretty good regardless.
As for mounting them, your rear one should have two handle shaped brackets with two holes in them that are part of a brace that's sort of inside the actual chrome bumper. If that's there then it's pretty well all you need for the rear. The front, by the looks of it looks like your missing either these 40cm ish long brackets that attatched to a similar inner brace and hold the bumper to the car by bolting to the frame rail. I should point out that both these inner braces are held on by bolts that bolt to those 4 chrome rivet like things on the outside, but I can't tell if they're there in your picture, sorry.
Anyways, looks like you've got yourself a sweet starting point there, + I've never seen someone with an 1974 LT before, so that makes it pretty cool
there couple of Hmong people around here also so thats pretty cool.
