Hard to say on filter flow. A good Wix 14x4- so taller than the standard 14x3 most single 4s run. And just an 850 4150 style carb feeding it. Now if you want to rate the carb at the higher test pressures like the HP series it would go as a 1000. Although they had a "Street 950" with the same contoured body and same booster/venturi size throttle blade size as the 1000! So a little playing on numbers going on. The old "original 950s were 750 venturi size and 850 throttle blade size.
I can tell you a few years ago I flowed a ported Pontiac E head, Torker II intake Holley 850 Trans Am Shaker air cleaner base with a plain paper filter and a K&N and the paper filter was only down 10 cfm on about a 300 cfm set up. And that filter is smaller than the one last night.