Check the casting numbers on both set of heads, all four heads, and post them on here That way we can see if they are all open or closed chamber heads and what the original CC where on them
You can also measure the thickness of the outer head bolt bosses to see if they have been cut or not also
CC each head is the best way to know exactly the size of the combustion chambers, don't be surprised to see form 1.0 to 5.0 CC variance on your stock heads, even on 426 Hemi heads
I have new set of 440 source aluminum heads in my shop now that vary 5.0 cc between all eight chambers
I have another set of them that had been CNC ported and cut down from stock thickness to get 72.0 CC for each head, the intake manifold had to be cut a bunch on each side to get the manifold to fit correctly, now those heads are being switch from a 440 block to a new 400 stroker motor, I'm having .050 cut off both sides of the new Eddy Super Victor low deck intake manifold now hoping that is enough