ARP main stud and oil pump clearance

The #5 cap has a larger mating surface and is more bulky because of the oil pump mounting. I just trim the stud and use the 12pt nut because I think there is enough strength difference between the factory bolt and an ARP stud and because the block was main honed with the ARP stud.
In regard to the bearings or chain - if the block was properly honed there will be no difference in the crank centerline, and no need for the longer chain or any special bearings. That being said, a chain tensioner IMO is always a good idea.