All front sheet metal is different, but will bolt on and match up to doors.
Doors, all other exterior sheet metal, except rear body panel will interchange.
Lower bolt in dash panel (gauge cluster mount), will interchange, but is different in switch spacing.
Frames and front suspension interchange.
Karl or Chris do the 66 300's share many parts with the 67?
https://eauclaire.craigslist.org/cto/d/1967-chevelle/6207527712.html
Doors, all other exterior sheet metal, except rear body panel will interchange.
Lower bolt in dash panel (gauge cluster mount), will interchange, but is different in switch spacing.
Frames and front suspension interchange.
Karl