[Fot] TR2 Cylinder Head Studs

[M&M Hado]

I was just finishing up a TR2 engine rebuild and one of the 9.5" studs
stripped the threads in the block at the bottom of the 4" hole when I got to
about 70 ft-lb.  Has anyone successfully put a HeliCoil at the bottom of
this hole?  

The original size of the hole in the block is about 17/32" (just enough to
accommodate the 1/2" stud, of course) and this happens to be the tap drill
size for the 1/2-13 HeliCoil.  The OD of the HeliCoil itself is about .615"
so that means I would have to drill out the hole in the block to something
larger than this - say 5/8" and save about an inch at the bottom for tapping
for the HeliCoil.  I'm wondering if there is enough meat in the block to
drill out the hole to 5/8".

Having gone this far, I really would like to save this block so any
ideas/hints/experience would be appreciated.

Thanks,

Mike Hado