I'm just trying to follow the logic.

'38-'52~ 216 US GM side of head is open to the lifter galley and has a tall galley cover,
'50-'53 235 US GM (previously military only) has the short cover.
'50?-'52 216 Canada GM also has the short cover.

Manufacturing head and block forms for a foundry are $$$ or CA$$$.
Could the early '50-'53 un-tooled blocks be bored out to 216 and 235?

"Adding CFM to a truck will only help at engine speeds you don't want to use."
"I found there was nothing to gain beyond 400 CFM."