Trick Flow 440 heads, The Real Deal?

The information sheet IQ52 posted shows minimum bore size of 4.32 inch. The bore size on my 383/432 is 4.28, that is of course .02 inch less radius...not much.
Is the trick flow minimum bore due to combustion chamber size, or valve diameter, or??
Can someone measure the combustion chamber diameter along the long axis of the head deck surface, IE parallel with a line thru the valve centers? Could they also measure the distance from OD to OD measured thru the valve centers? This should be slightly less than the combustion chamber measurement.
thank you.