Are you sure about the front fender's?Can't say much bad but there are differences.
1971 you had to pay more for the deluxe interior was not standard. 351 way more desirable than 302. 6,121 of all models and engines made in 1971. Of course the Q, R, J and C codes are pretty rare. It is sort of odd that the H code with 3 speed only had 85 built.
All 71-73 verts have power top and glass rear window. You had black or white top only. The front seats are different for 71 and also the rear seat belts and side panels are different. PW for 71 72 are the same.
1972, This year you get the deluxe interior at no added cost. If you go to the Ford Facts Book on the site will tell you all the standard items that come with convertible. Again Q and R codes are rare but again the H code with three speed only built 82 of them. I have one of them was crashed so just a parts car now. Several members here have Q codes, I have one of the 330 with automatic. When you ordered the Q code in 72 you got the NASA hood. You could get the side stripes on convertible if you got the decor package. Decor group got you Mach 1 grill and black out of lower& rubber front bumper. You could option a vert with any option you could get on Mach 1 with the exception of the Mach 1 name, honey comb rear panel and plastic carpet insert. PW option same as 71. So there are so well optioned verts out there. 6,401 total build.
1973, Again you got the deluxe interior as standard. No R codes no CJ best was the Q code which was called out as 351 4-V on window sticker and air cleaner. There are a few little differences to the 72. Heavier front bumper to pass the crash test. The Q had smaller intake valves. Toward the end of year the factory that did the comfort weave material burned so some have odd interior codes. Again you can option one out to be what ever you wanted. Ford Facts Book is specific to what you could get. 72 PW has different switches and bezels that are common to other Ford models so easier to locate NOS parts. 11,853 were built so maybe a better selection of cars and parts for this year.
I drive a 73 vert and building a 72 Q block sanding now.
The fenders, hood, doors, are common to all models. Glass in doors are different all models. Windshield different. Trunk on vert same as coupe.
71 - 73 rides and drives much better than previous years. Just like any mustang you need to do in person review of any car you are buying. Check for rust and correct parts on car really kills value for small engine and rust and not numbers matching.
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The 73 model year fenders are different from the 71-72 model years because of the bumper redesign. As David said, the fenders are common to all models in a given year.Are you sure about the front fender's?