904 Front Pump Bolts

I tried looking around at the hardware stores and they have some 5/16-18 bolts, 1-1/2" long that are the right dimensions except the head. The problem is they only have seem to have plain hex bolts that match up, whereas the pump bolts are washer head bolts. Do you think throwing a stack of washers on the hardware store bolts might work? I am just concerned about that having the potential of causing leaks.
yeah that's starting to sound a little sketchy LOL we better find you some stock bolts...