"Thank You " Bluecar............some of these guys want to make this a "Space shuttle" project when a simple gas torch is the easiest way !!!! & some on here I guess didnt read that he has no access to a welder , but will rent a gas torch !!!
Many machine shops now have the sonic disintegrators. They just push the probe against the stud or tap & buzz it out of there. It really works well on the taps since they are so brittle.
Thanks for all the help guys. I had pretty much decided on the cutting torch, I just wanted to see if there was something I'd overlooked. I'll get on to that this week.
If the torch doesn't work and the tap is bottomed tightly in the block, then as Rotorwrench mentioned, an EDM (electro magnetic discharge machine) is probably the answer.