Heres picks

use a drill , drill a small hole in what is left of the bolt. then tap in a extracktor that should get it out.as your trying to remover it use a little heat.

Do not use an extractor....or you will have a broken extractor in your broken bolt.  Extractors work if the bolt broke under tension, not if the threads are seized. 

I'd set that thing up on the mill with a rotary table so I could use a few of the good holes to reference the true center of the bad hole, then go at it with carbide until enough is removed to pick the threads out.  Depending on their condition, a time-sert may be required.  If you're near long beach, I can do it for ya.

Thanks guys I thought I could get lucky and not pull the bowl
But no go
I'm going to pull the bowl and take to a buddy's to set up on the mill

Thanks for the offer pat!

Chris

If you have access to an ocy acetaline(sp) torch. Use a small tip and heat just the broken bolt. When the part is warm (i would say just at red)  quench the whole thing. The two dissimilar metals will expand and cool at different rates, and should break the bolt free. Or you could melt wax into it. They both are a stretch but, both ways do work. Very old school but effective. I have had to use both methods many times on some of the older cars we restore at my shop.