I've been going through this exact same problem.
I snapped a bolt off so bad removing my water pump, that I had to yank the engine, and I essentially decided to build another engine. Screw those GODDAMN water pump bolts.
**** arp too, they are a joke. I called them, and asked them if their kit came with studs, and the dumb lady on the phone says "we don't make studs". I said, HUH? Then I asked how in hell you're supposed to bolt your accessories on with their bolt kit, and she said, I don't know, we don't make studs.
Please, update me with that stud kit from vatozone.
Another option is to just get some length of simple hardware studs, and thread it into the block, cutting it at the right length, then simply screw a nut down. No reason why the nut has to be secured on the stud.
I went to the yards last weekend, and found an 89 gt, and all of the water pump bolts were actually loose, pleasant surprise, so I'm going to use all of those