Need Help!!! Lost 5.0 water pump bolt. Are all the bolts the same diameter?

Hey guys,

Been gone for a while, but back in action again. The 514 is now machined and bottom end is buttoned up, but I guess that has nothing to do with this, so anyway, on to the question..
My buddy called me over to help him put in a new radiator and put back his stock water pump, when I bumped into an issue.
There are 7 bosses on the pump, and he only has 6 bolts, (he thinks he lost one) but the problem is, the boss next to the outlet port on the timing cover doesn't seem to accept any of his other bolts. (I know there are different lengths, but are there any different diameters, or are all the bolts the same diameter?
Its an 89 btw.

Any help would be appreciated

Regards

Matt
91 coupe