Ordinary carb studs would probably work perfectly. The threads in the water pump flange are 5/16-24 UNF (Fine). Summit sells a kit for $4 with 1-3/8" long studs. (They also carry 1-3/4" and 2" and 2-1/4" and 2-1/2" and 2-3/4" and ... if they end up too short.)



Obviously you'd want to lock them in the flange, but a nut on the back side of the flange would work, too, if you get them the right length

Carb Stud Kit