Nice seeing the 2.11 clear that small bore. As Squidward says,
deck clearance will change depending on casting used.
Now here's the $60,000 dollar question: at what point do you
sacrifice valve lift for compression? There's like 20cc worth of
difference between the late 6X-4s and early 17s (IIRC).
And if it's just some bowl blending, you could add a big valve
to a '69 47. There's enough variables to make one's head spin,
but it's all so very intriguing.