In regards to ' 68-'72
Dash - '68 completly different in shape and design, '69-'72 same
Doors - '68 inside door lock pull place at rear edge of door , '69-'72 door lock pull moved about 6" forward
Bucket Seats - '68 release button on seatback side/top and no headrests, '69-'71 release on seat back center w/ headrests, '72 highback buckets
Door / Side Panels - '68 different design, '69-'72 same with only changes in the colored strip across top area ('69 parchment, '70-'72 woodgrained)
Seat Upholstery - '68 different, '69-'72 very similar
Hood emblem - '68 says Chevy II, '69-'72 same w/ bowtie design
Grille- '68-'69 same
Headlight trim - '68 no adjustment hole and chrome, '69-'72 with adjustment hole, blacked out
Front bumper - '68-'69 small turn signals, ''70-'72 large turn signals
Taillights - '68-69 short design, '70-'72 long design('72 has different lens)
Rear trim panel (fills area between tail lights)- '68-'69 longer , '70-72 shorter
Decklid emblem - '68 "Chevy II", '69-'72 "Nova"
Side Nova emblem - '68 "Nova" rear quarter panel, '69-'72"Nova" front fender behind wheel opening
Side marker lights - '68-69 small lights (red rear, front '68 clear, '69 Amber) '70-72 long design 9 amber front, red rear)
Fender vent optional on '68-'70
'68 SS only has "Super Sport"on bottom of fender above rocker trim
'68-'69 external anntenae, '70'72 anntenae wire embedded in windshield
The '73-'74 same size and body shape, except dfferent. different side window open shape, front and rear, impact bumpers, hard plastic interior, hatchback offered - hood and fenders are the same as '72 (fenders have a filler bolted on, trunk lid same
Hope this helps