[shorod]

For starters, are you sure there's room for a longer bolt in that hole? Often those bolts break due to being seized in the timing cover (galvanic corrosion) and not necessarily from being seized in the block. So I'm not so sure, unless you've already checked, that a longer bolt would make it to the block. Also, if you're not threading into anything it doesn't really matter how long the bolt is, it's not going to be providing any sealing force to that area of the water pump. Your more effective place to put a sealant (and not JB Weld) will be the gasket surfaces between the water pump and gasket and the gasket and timing cover. Let the RTV gasket maker partially cure per instructions, install, then allow the full cure to happen. Properly torque the bolts that still thread into metal. At that point, putting bolts into the holes with broken studs is purely for appearance.

-Rod