If your gonna give advice on how to port the XS head I would strongly suggest you educate yourself on HOW TO PORT THE XS HEAD first. Spent seven years and LOTS of money to educate myself where to abstract to most gains out the XS head with what little the factory gives you to work with. Are the ports really to big to begin with? I 'll argue with you all day on that subject cuz quite frankly it's hard to argue with hard cold facts of the XS knocking down 45 to 60 plus MPG with those so called oversized ports
.For racing purposes with cam lifts of .420 plus KNOWING where the XS flow begins to diminish in flow curve would in deed have some truth to the oversized ports that you speak of but for normal street hot rodding where the lift ranges fall between .360 to.390,the normal sized ports will do just fine and again get some real flow time under your belt and only until then will you begin to understand how and where and what makes the XS head a better performer, I know I do