Success!
I have been working on the same project (off & on) ever since I bought my boat. Last week I finally succeeded.I finally gave up any hope of ever removing the bolts and tried grinding the bolt heads off using a dremel tool with a high-speed carbide bit. That didn't work too well either but occaisionally the bit would slip off the bolthead and down to the lip of the SS housing that supports the compass. I didn't want to destroy the housing (Ritchie, the maker of my compass, also makes the housing, and they call the housing a binicle. The also wanted $104 for a new one if I had decided to destroy it to get to the frozen bolts.) Anyway, by grinding away a narrow portion of the housing that surrounds each bolt I was able to lift the housing straight up over the bolts. Once the housing was off I used vice grips to remove the bolts.To put it all back together I used extra wide washers under the new bolts. These are big enough to span the large holes that were ground out of the housing.Dont forget to use anti-sieze compound on the new bolt's threads when putting it back together so that the bolts can easily be removed next time. If it had been assembled that way to begin with it would have saved us both a lot of trouble.