<VV> Busted head stud, what to do???

[Edelstein and Payne]

folks,

     My son Doran and I are prepping a block (crank case) for the engine in his 65 "hotrod", and 3 of the studs had a fair number of the threads at the top corroded away, so we decided to replace them.  We have spent some weeks spraying PB Blaster and then the half ATF/half acetone pentrating solution that was discussed here some time ago, without success.  We then tried to heat the aluminum around the base of the studs with a propane torch, also without success.  Then we heated the whole block to 450 degrees in an oven for an hour or so (moms was away for the weekend), and with a "stud puller" at the base and 2 jammed head nuts on the top threads with a wrench on them, we got one loose.  I then kept working on another one for an hour or so (obviously the block had cooled)and managed to snap it off just above the bottom threads.  (Needless to say, we will leave the third one alone.)

     So it looks like I have to drill out what remains of the broken stud.  Any tricks or advice on that?  Is it possible to drill it out and maybe save the threads in the block, or am I now relegated to doing a heli-coil installation?  And it seems like I remember something about the threads in the block being "special" to create an "interference fit" or something with the studs.  Am I hallucinating about that or is it so?  And if the threads are special, then what kind of heli-coil do I use?

    Many thanks for any help you can give.

               Travis Payne    65 Monza coupe
               Ralegih, NC     65 500 coupe