the problem is that most of them are pretty long. the 2 at the bottom of the water pump are SHORT!!! they only thread into timing cover. A certain someone I know threaded a bolt that was too long and cracked his Cam timing gear, and found out after he cranked the motor....
I only see hime when I look in the mirror... wierd.
anyway, I know that the heads are all 9/16"
I will also say, take a close look, there are a few bolt holes you cant get to when the water pump is on.
Good Luck!