Originally Posted by billhendren
They make tools to drill and tap your block straight but if you cant find one you can make one if you have access to a mill. take a piece of steel at least one inch thick and drill a hole in it thats the tap drill size,then drill another one next to it and tap that one.on the other end cut a slot that is wider than the 7/16 bolt.position the slot so it will reach any other head bolt. simply center the fixture up on the bad hole and bolt it down.using the tap drill size hole to square your hand drill,drill the bad hole to tap drill size. loosen the fixture and position the hole you tapped over the bad hole and clamp it down. screw the tap through the fixture and into the block.thats all there is to it.Bill
....This is the preferred way....I did mine with a friend an electric hand drill....a metal square.....and alot of luck....you have to make sure the drill is square up and down and side to side....go slow and be patient....drill out the threads and we helicoiled it i think it is 7/16th treads and repair kit is available at local parts stores for bbc...then insert thread repair and locktite it in....then do not over tighten the head right away go in stages and slowly torque this bolt to specs....good luck