Is the car a 69 Firebird 400? I believe the FB 400's came with a 19/19.5 inch fan. I have one on mine that is stock, but I may be wrong. This is from the AMA specs. https://firstgenfirebird.org/firebird/1969/ama/ama_page3.html#coolingsystem
7 blade 18 dia. Poer-Flex fan on 6 cyl. with A/C.
7 blade 19.5 dia. fan on all V-8 with A/C
5 blade 19 dia. Power-Flex std. on 400 V-8.except std.
4 blade fan used with Ram Air Option.