I found several complete old car owners manual scans. Interesting to note oil recommendations, and surprising to me the SAE 20W recommendation for summer conditions.
1950 Mercury:
http://www.tocmp.com/manuals/Mercury/1958/Owners/pages/50MercOM 24-25_jpg.htm
1957 Chevy:
http://www.tocmp.com/manuals/Chevy/1957/Owners/pages/25_jpg.htm
1960 Dodge Dart:
http://www.tocmp.com/manuals/Dodge/1960/1960DodgeDartOwnersManual/Page052_JPG.html
1960 Ford:
http://www.tocmp.com/manuals/Ford/1960/pages/60 ford_page 55_jpg.htm
1968 Buick:
http://www.tocmp.com/manuals/Buick/...ages/1968 Buick Owners Manual-Page 50_jpg.htm
1950 Mercury:
http://www.tocmp.com/manuals/Mercury/1958/Owners/pages/50MercOM 24-25_jpg.htm
1957 Chevy:
http://www.tocmp.com/manuals/Chevy/1957/Owners/pages/25_jpg.htm
1960 Dodge Dart:
http://www.tocmp.com/manuals/Dodge/1960/1960DodgeDartOwnersManual/Page052_JPG.html
1960 Ford:
http://www.tocmp.com/manuals/Ford/1960/pages/60 ford_page 55_jpg.htm
1968 Buick:
http://www.tocmp.com/manuals/Buick/...ages/1968 Buick Owners Manual-Page 50_jpg.htm