Is the thread in the block stripped, or is the bolt broken? If the block is stripped there's a product called a "Heli-Coil" that involves tapping an oversized thread into the stripped-out hole, and inserting a coiled-up piece of spring steel to bring the thread back to its original dimensions. The installation kit is pretty spendy if you're only fixing one bad thread.
Option #2- - - -drill and tap the hole to the next larger thread size. If it's a 1/4"-20 now, go to a 5/16"-18. The bolt head size will change from 7/16" to 1/2".
Jerry
