Joe Attardo provided this information:
Up to 1980
Item
Hayden P/N
Thermal Clutch
2705
Non Thermal
1705
HD Clutch
2747
Napa 271303
ED Clutch
2797
271301, 771301
Fan
3618
Flex Fan
3568
Heavy Duty Flex Fan
3718
Fan Spacer
3962