302 heads-Is it worth putting them on a stock 318

A couple of posts ago it was talked about "68-9" and "89-91" 318s and their CR. Actually they advertised 9:1 from 85-91.
But I have to ask, how "true to form" are those numbers? I've cc'd a couple of different engines plus reading of others doing the same on a rebuild, and stock, unmodified they usually come out short of what's advertised in the manuals.
Between the pistons not being as close to TDC as they could be (or are advertised as being), and combustion chamber volumes actually being bigger than advertised, unless you blueprint it and machine parts as needed, you probably aren't getting what you think you are.