Rule 201 c. A correct* 327 Chevy can use a 350 or 400 block, if it appears externally correct*, and is made from the correct* material.

I think this falls in the "upon a cursory visual inspection by someone reasonably familiar with the year, make and model claimed, it looks like a correct* part"

My guess is that an extra freeze plug, a different shape accessory boss, a slightly different timing cover design, etc would not be considered out of spec for the rule.