This is only speculation from my side. If you had 4" bore vs 4.3" bore it would be much more equal I think, over 300cid should not have less than 4" bore to get a big enough valve to feed all the cubes, if big power is goal!
If the valve is very close to the cyl wall, you not only get less flow, but it may restrict the amount of lift you can make before the valve hits the cyl wall.
But I dont know anything about that, you must try and test. But if you cant open the valve more than say .400 before it hits the wall. It would not exactly increase performance.
A shrouded big valve probably flows less than an small un shrouded valve, and the shrouded valve makes poor swirl since everything "chrashes". Unless maybe the wall for some reason increases swirl, who knows?
But it does matter what valve angles and center placement it has. And not forget about how the "TEA" combustion chamber diameter fits to gasket and bore.
With an head that fits well on both engines it may not loose as much power, but if you take advantage of the bigger bore on the big bore engine, that one will probably make best overall power, and more total.
How much power do you want? 350 or 450, 600 or 800?
I can try to make an graph in Engine Analyzer where I change nothing but Bore and Stroke and leave everything else equal. To make an comparison if you want.
Big bore = More Flow = More Power. Add a long stroke to that and it is win win!
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