So far no luck at getting the broken tension bolt threaded end out of the front casting.  With help from Cary Beazley, we were able to back out the broken part a little bit with just pressure and mating the two surfaces together, until it jammed and would come no further.  Not having (or knowing about) LH drill bits at the time, we decided to RH drill a pilot hole for an easy-out.  Drilling the hole was no problem but getting it centered was, so it’s drilled off-center and the broken piece is now probably bottomed out in the casting.  The easy-out is simply not latching onto the bolt.  We’re going to borrow a bore scope to get a better look.  After that I’ll have to make a long center-punch and try to make a new (centered) pilot hole with the long LH drill bits on-order (see link) … hopefully they’ll grab onto the part and extract it, otherwise it will be an engine tear-down, which I dread at any time but at -10C it’s no fun at all.