Only certain head/block combinations need the drilled head bolt. It's located in the center hole on the passenger's side, and the bolt has a slot in the top resembling one for a big common-blade screwdriver. Early-production heads have an oil line feeding the rocker arms, while later ones use a drilled oil passageway in the block and a corresponding one in the head. Certain combinations use the drilled bolt to complete the oil circuit to the rocker arms.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!