Is the intake still on the head? Is the head on or off the engine? What is your location? Some bigger citys have EDM machines that can burn out the offending bolt and easy-out. Costs about $20-$30 and saves the threads.
Also, if some bolt is sticking out, you could slot the end for a screwdriver if theres not enough to grip with visegrips and you don't have a welder. But before you do that, heat the bolt and head up with a propane torch and hit the edge of the hole with a candle, the wax will melt down between the threads via capillary action, let it cool and usually you can remove it with a screwdriver.
I agree with those above, welding a nut on the end of the bolt works pretty good.