the holes that are circled are for the guide pins.
the other [larger] threaded holes are 7/16-14 [course as has been mentioned] and the smaller holes are 1/4-20 thread.
the top threaded hole above the starter gets a stud that is 7/16-20 [fine] thread the starter hangs on. there is approximately 1 1/2" of stud hanging out of the bellhousing. [calibrated eyeball measurement ]
i just double checked this on a 727 on the shelf.