Seems to me that is one of the least stressed and/or strongest part of the block so the stock bolt there would not be so bad. And you could take the flat washer out; just make sure the bolt does not bottom in the hole in the block. The washer helps to make the bolt torque more consistently but I would not be afraid to eliminate that one and back off the torque a smidge; you still have the ARP lube at that point to help make things torque smoothly. Edit to add: I assume this is not a super high powered engine.
