The foreign stuff is JUNK, Wally. Goodmark is touted as the best US seller of replacement sheetmetal, but they're made overseas, too. I replaced the fenders, doors, tailpan and deck lid on my '68 with Goodmark stuff, and none of it fit like genuine GM. One set of fenders was so bad I had to send them back and get another set. The biggest problem was that many of the body lines and gaps between panels were way off. The left fender eyebrow was so far off that the headlight door wouldn't even fit into it! I had to elongate holes in the tailpan to get the taillights to fit. When I shell out those kinda bucks I expect things to FIT! Don't expect perfection from the repro companies.
My advice is if you can find genuine GM NOS or used sheetmetal, buy it despite the cost--even if used parts need patch panels. It will save you countless headaches. You should be able to find some stuff at Carlisle.
Several restoration companies sell repro GM assembly manuals that will tell you the gap specs on body panels as well as almost all other components. I got mine from Rick's 1st Generation, but Year One sells them, too. Year One are great people to deal with!
Hope this helps.