Check bore diameters 273 versus 318. I know valve shrouding can occur just not sure where. Maybe its 915 heads that conflict. Either way , better safe than sorry.
You can drill the stock intake holes with a hand drill ( others have ) . I think I would set the intake up in a drill press or milling machine to correct the hole angle. To do it by hand doesn't guarentee the bolts will all start straight and pull down correctly. The land angle under the bolt head is just as important as the hole.
