From what I've read so far in the book I mentioned earlier, square ports have poor flow characteristics. I think the only reason most manufacturers use square ports is because of space limitations. Chev did it because of the pushrod location. I think the book even mentions filling them to an oval-ish shape drastically improves the flow. Definitely worth having a look at the book.

I thought the same about square ports especially on whoreden sixes
but was told different by the developer of the rotary valve engine
for the Caterham who pointed me to late aftermarket chev heads which
have no spacing constraints and also some yamaha engines.
Im sure the chamber and so many other aspects play their roles but
the Japenese sunny engines used very rounded big ports.

A15 head ported -- kale said it "flows enough for 160hp"

turbo yes but NA that wouldnt flow more than 120hp no matter the block
the cam, revs or the optimistic dyno.

Yes you got that right. When he got it dyno'd it was only 110hp at the wheels

LOL cause that guide treatment creates swirling on the back of the valve
impedes flow by interfering with its path on entry. Stock port heads can
make 110hp atw with just cleaning up the slags, clever Nissan engineers