I totally agree on the filler part. These cars have lead fill , and later ones have body filler in the stock seams in the roof , and where the quarter meets the rocker panel. I have used filler, but i like to keep it to a minimum. I had a large area that was dented in that i pulled with a stud welder, and got close, then i filled it. It looks good in primer, body lines look nice too. , but i also patched rust thru, and lots,of parking lot rash.
If the goodmark ones dont fit well, my option is to spend some extra cash and get the AMD ones for a fastback and cut them down. I do autobody as a hobby / side job. Small collision repairs etc. i have hung rear quarters on several old cars and dont mind spending the money for the better panel. The good mark ones have been around for awhile, but i dont want to pull the trigger on these if im not gonna be satisfied with the fit and stamping quality.