I'm doing my first port & polish job on a pair of aussie 302C heads for my 351C. I noticed that one cylinder on each head has a rectangular port connecting the exhaust valve bowl to the intake manifold. I can only guess that this is some kind of emissions reducing feature to reburn part of the exhaust, similar to an EGR valve. What is this for and what's the right way to polish it? It's got a huge casting flash along one edge that I figure I should grind down, but even then this gaping hole is bound to cause a lot of disruptive turbulence in the bowl. What would it hurt if I was to fill in these ports? Thanks in advance.