86 Olds 442

As I await my 307 cam swap , I am playing with numbers.... 307 Cylinder volume is 38.37 in3. With the new cam, calculating the area under intake valve with new lift multiplied by degrees open I get 99.6% of cylinder volume, where the original was 85.6%.
I may have fluked myself into "max efficiency... now intake opens at 1deg ATDC but closes 31 deg ABDC, so this calculation is somewhat bs, but has anyone looked at this for any given engine when selecting a cam? Just curious.