the top four unthreaded holes are for the 3/8-16 thread bolts that thread into the engine block. these, you know.
the two threaded holes you need bolts for are 7/16-14 thread. however, i am not sure of the length of these. "possibly" around 1 1/4" or 1 1/2" long. i'm just guessing on the length of these bolts.
i believe the starter bolt threads are 5/8-11 thread.
hope this helps out.