In my experiences, 200-210cfm is enough for about 400'ish HP, 300cfm ~ 600hp, etc. About 2HP/CFM on pump gas street/strip motors V-8's. E85 will make a bit more. well built/tuned examples will make more, more average examples will be less.
As for headers, I have Steve C.'s old BIG D-ports I'm not likely to ever use. Part number 35145, 1-7/8" primaries, 3.5" collectors. They have an adapter flange that bolts to the head, then the header flange bolts to it (wider bolt pattern).
https://www.hedman.com/product-detail/35145 Coated inside/out, with a higher quality coating than I've seen on most other headers.
I think I paid Steve about $370 for them?? Maybe he remembers :-)
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'73 T/A (clone). Low budget stock headed 8.3:1 455, 222/242 116lsa .443/.435 cam. FAST Sportsman EFI, 315rwhp/385rwtq on 87 octane. 13.12 @103.2, 1.91 60'.
'67 Firebird [sold], ; 11.27 @ 119.61, 7.167 @ 96.07, with UD 280/280 (108LSA/ 109 ICL)solid cam. [1.537, 7.233 @93.61, 11.46 @ 115.4 w/ old UD 288/296 108 hydraulic cam] Feb '05 HPP, home-ported "16" D-ports, dished pistons (pump gas only), 3.42 gears, 275/60 DR's, 750DP, T2, full exhaust
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