I hope this helps a bit. The Corvette Parts Interchange Manual says
69, 70,73, 74, 75, 76 , 77, 78, with AC had 17" 7 bladed fans. It's possible they might interchange. Here are the part numbers
69 3955182
70 3969926, 3993889, 3991427
74, 75, 76 L82 342715
77, 78, 79 469580
76 l48 342501
73 BB 3992095
There are some big Vette junk yards around the country, you could call around.
Or go for an aftermarket flex fan.
Good luck