Look std valve size to me, but as said way too dry at top end, don't open holes out as it is not needed if you have decent oil pressure which I suspect you don't.
If a cam with a lesser base circle is put in it will need extended ball studs, very cheap and a very common reason why they get ripped out, just check the thread on the head now where it goes, though normally is ok, I had it once, so changed to all extended ball studs, still have my old one in my nasty collection as well.
tabetha