Go over to their website, https://www.airflowresearch.com/, and read the specs on each head. I believe the 165 uses the smaller valves. 1.90 intake. 1.60 exhaust.
The best flowing iron 289 vintage heads were the GT40 heads. Those flowed around 240. The 2x4 Holley T/A manifold matched it. That is quite a unique manifold. Nothing exists quite like it. It ran two Holley 735cfm center squirters.
When the Boss 302 heads were introduced, they became a revelation because of their flow potential. In his testing Dan Jones flow tested iron "Cleveland" heads at 296 cfm @.600" lift.
The dyno test that I posted here showed 539 @7,000 with Webers on a iron head 357 "Boss 351".
The iron J heads flow around 180 stock. About 215 professionally race ported. The AFR 1388 shows flow results of 295 @ .550. Using those, you should be able to get similar results to that Cleveland, with similar cubes, similar data?
Induction is another issue.
I chose to go with the T/A 2x4 Holley manifold with two 600cfm 1850 carbs. .550 lift cam. 347 cubes. Whatever the number it's making, I'm happy. It causes quite a scene and adds to this local tale of a crazy old guy in a white Shelby. It's a little like the story of Washinton Irving's tale of the 'Headless Horseman'. Appearing occasionally late at night on spooky moonlit nights scaring the wits out of the innocent locals? But that's how I get my jollies.
That "T/A" intake carb combination is worth about 50 hp over any single 4v set up that was tested. Webers are pretty well documented at around 80-85hp.
I have no idea what the original 302 4v iron intake and Autolite carb actually do flow but it likely is complimentary to the stock flow of the iron heads, i.e., not much? I'm sure it's likely a huge restriction to making any kind of power expected of even street engines today.
I never did flow testing on that set up and don't recall anyone else publishing information on that? The best "stock" induction that I saw for the J engine is the S7MS COBRA single 4v high rise and the S8MS 600cfm Holley carb for the 68 Shelby GT350. It changed the characteristic of the J engine and made it "sporty".
Acknowledged, building an engine for a Mangusta does raise a bunch of questions that only the present owner can answer. It all depends on what they want out of the engine.