Philip: I do not know of a reference or source to find the nominal size/flow volumes for intake or exhaust for your castings. The best I could suggest is that you take them to a Head shop. Preferably one that does speciality work and porting. They will have a buret and flow bench and could measure them for you.
The castings that you have 462624 are in reality just run of the mill SB 350 mild heads. That is if in fact, they are factory original 350, they would have the larger valves, but they would have large combustion chambers and poor port/air flow. But still, just average heads. If you are looking for performance out of your SB, there are three heads that are highly recommended by the Chevy experts, that the SB came factory equipped with. They are:
1. GM/casting number 3782461 1961-1970
283/302/327/350 1x4, 2x4, FI 62.1cc c chamber
This head with 1.94 intake and 1.5 exhaust was used in the 275,300, and 315hp 283. Also used in the 300, 340, and 360hp 327. In later 60's (65-66)
was fitted with 2.02 intake and 1.60 exhausts. Was used on later 60's 350, 365, 375hp 327's. Same head was used on late 60's Z-28 290hp 302. Same head was used on late 60's LT-1 370hp 350. In the later heads only the valve size was enlarged, the ports and chambers are identical.
2.GM/casting number 3991492 1967-1973
302/327/350 1x4, 2x4, FI 66cc c chamber
This head is sometimes called the "fuel injection"
head. Came in two versions an early 302/327/350 with straight spark plug holes. Later model was angled plug holes. This casting has the good stuff like screw in rocker studs, pushrod guide plates. Chevy engineers claimed that the angled plug gained 10hp over the straight plug version.
This head also came in two valve versions with 1.94 and 2.02 intakes and 1.5 and 1.6 exhausts.
Was used on 275, 290hp 302. The 300, 340hp 327. Was also used on 325, 360, 370hp 350.
3. GM/casting number 340292 1973-1980
350 1x4 and FI 66cc c chamber
Called the "Turbo" or turbo angled plug head.
Came only with 2.02 intake and 1.60 exhaust.
Have screw in studs, guide plates, larger spring seats, and larger ports. No heat crossover passage. Usually equipped with the larger springs.
On top the valve spring seat was enlarged from 1.28 inches to 1.44 inches. Also has enlarged ventilator openings (pushrod openings) for increased crankcase ventilation. The combustion chamber in the 292 head is identical to the
There you have it, hope this helps.
Think Chevy! :p