I like the old guy tip I learned when I was about 20is of using a Dremel tool and the bolt extractor combo. Last time I had to get a bolt out was someone that sold me a Weiand Stealth manifold for a giveaway price, and the only thing wrong was a snapped water neck bolts the guy couldn't get out. Just use the Dremel to grind a pit in the center of the broken bolt, use the left-hand drill bit to drill a hole for the extractor, and most of the time the drill bit will get the bolt out. Keeping it simple cost so much less in frustration, and sometimes cost way less on the bank account.
Good luck