The '67 and '68 had Frame issues as well, but mostly only from rough weather states. I would have to check the book to be sure, but I believe all the Frames are the same except for the Convertible, year to year. Different year Frames will interchange, but there are some differences. You would have to check into the specifics before using a Frame from a different year.
-Parting Out over 75 '58 to '73 Full Size Chevy Cars-
-National Impala Association
-Vintage Chevrolet Club of America