better iv you as chris (350ep70gr) he knows the answer
the tolerance will be the same as normal 4e headbolts, just different size
you dont have to drill them but its a a tight fit as there never dead stright i had mine done .5mm and you will need to make the holes in the gasket bigger plus you need to cut 2 down so they dont hit the cam gears and mill the head out to get a 12mm scoket in there its a lot of fucking about what power you going for
Is there a known fault with using the E series ARP head studs?
I dont know of any, except for people over tightening them that is.
So why bother spend the extra money & time, when its just not necessary.