I assume you got a 70 challenger grill....thats a good price if its in good shape! the 72 fenders are totally different inside where the headlights mount up...there are several things you have to do including welding the 70 headlight bracket in...and finding the brackets to mount it.....good luck...I just bought 70 fenders because it was cheaper to buy a nice set of used fenders that it was make the 72 fenders work 72blunblu talked about it on the first page.....
Well, I wouldn't say the fenders are totally different. The only thing different is the headlight bracket. The inner structure of the fender is the same. There may be a few mounting holes missing from the '72+ fenders, but the structure is all the same.
Here's a picture of my '72's fender...
And here's a '70/'71. This is the headlight bracket and inner structure that was removed from the fender. You can see the inner structure behind the headlight bracket is the same, the headlight bracket just spot welds to the inner structure.
This is the other side from the bottom, you can see how the headlight bracket is spot welded into the inner structure.
So really, all you need is a set of headlight brackets like the one's BEA sells that I linked on the first page. They're not an exact match, you can see on the originals there's a long tab that extends forward, but it's not mission critical. The BEA parts bolt in too.
To that end, I actually removed the headlight brackets from the inner structures I had and sold them separately, putting them up side by side with the '72 and '70/71 fenders made it fairly obvious that the headlight brackets are the only major difference. Some of the holes for the latch panel and such will have to be drilled, but the metal is there.