Pardon me, I don't have a clean engine apart where I can examine it.
IIRC the pushrod clearance (and oil drain) holes in an 18 bolt head are 9/16". McGurk suggests enlarging them to 3/4" for bigger pushrods, but is this true for both the 15 and 18 bolt heads?
The holes directly below them in the block deck look considerably bigger, but:
1. are they?
2. how big, 11/16"?
3. are they accurately aligned with the head drains, or just bigger so they can be sloppy?
Thanks (yes, this is for the book)!!
