Just tossing around some ideas in my head about heads. A 340 with a non T/A 3418915 head has 1.88" intake valves. Take the same exact head & use a 2.02" intake valve. With everything else being the same in the engine, which one would have more power & torque? How much would you gain with a port job on the 2.02 head?
Let's say they go on a 1969 engine. I know I'm being somewhat vague with the rest of the engine. If the engine is almost stock and has run a 12.19 @ 109 mph in the 1/4, could/would you expect to pick up any in et & mph by switching to the 2.02" heads? Just curious about what you think.

Im not a head guru, or a guru of anything else, thats why im always on here asking ???'s. But i have heard and or read that small valves like mild to moderat builds with 55 to 62k ish shifts, big valves like more everything to make power, not much info but maybe it will pull in a more knowlegable chimer.

In your example, the 2.02" valve would help. Reason being, a
bigger valve provides more in­­² of curtain area. It would also
help if a valve job was employed to enhance the air flow at
the valve lift your camshaft dictated.

Porting helps too but, is more advantageous at higher lifts
and engine speeds. Then, you'd want to use a valve job
tailored to that use.