I believe your getting different peoples opinion of what shape the exhaust ports are & it's making it seem worse than it is (unless these heads have been intenionally ported to some square shape other than stock).
The Vortec heads use a traditional gasket & header port. Yes some gaskets & headers have wee little round ports (1 1/2" tubes), but the normal ones have a 1 5/8" tube which is bigger than a regular SBC port & also the Vortec. You have little to be concerned with assuming you buy a quality header that fits your truck.
Here is a stock size Vortec head...I have done some portwork in the runner, however the port exit shape & size are factory. The second picture is my 1 5/8" tube headers...the round area is just bigger than the squarish shaped port. Hope this helps. Lorne