Unless you're gonna do ONLY dragracing w/ engine rpm's primarily over 3000 rpm, all the tech. sources I've ever heard from say to do 'em. My last builder chose not to do them, but I had them added because it's cheap insurance for a "street-driven" setup that will spend alot of time under 3000 rpm. I checked with my head supplier,and because I live close by their Main office-they said bring 'em in and we'll drill them for free, which they did! I agree with what the head designers/supplier say.
Remember of course to choose headgaskets that have the steamholes, as some do not. Fel pro 1014 and 8634 do have them, 1004 and 1034 do not. -Jim.