The problem with the Ga heads isn't the flow, it's the goofy valve angles.

Ga 409100 [same number as G head] 80cc 2.000, 2.072" 1.625, 1.685"
1972 455's, including W-30. Valves almost universally 2.000 and 1.625", even 442's had small intakes, if auto trans models. Even the Toronados were relegated to small intake valves this year. Only 442's with W-30 or MT had the larger 2.072" intakes. No way to tell valve size without measuring a valve. Strange combinations of exhaust valve sizes and angles, depending on application. Weird combination of valve sizes and seat angles that no other heads matched. This might make finding valves more fun, should you need them. Exhaust valve with a unique 1.685" diameter and 30 degree face. All Ga heads use valve rotators on all valves, therefore have all deep spring seats. Hard exhaust seats.