chevy hi performance magazine has a good article on drilling the steam holes and it looks simple enough, as long as you get the correct angles. i was on a pit crew for a guy who threw a set of rebuilt 305 heads on his 350 with little luck, warped and cracked them in the first race he tried them. this is the only experience that i have had with them but if you would like i could find the article about drilling the holes and give you more details