If the threads are toast, you can try out a Mavic BB instead. that does not use the threads on a BB but uses angled retainer rings that tighten against bevels cut into the faces of the BB shell instead. They were sold in the 80's and 90's, but lots of them still pop up at ebay for auction. You will have to find a bike shop that has the correct Mavic cutting tool(s) to cut the needed bevels on your BB faces. Look to spend about a hundred bucks though, for an NOS Mavic BB....plus the cost of the BB face beveling at the bike shop. Could be worth it if your frame is a good one, as the Mavic BB is high quality. I beleive Velo Orange also sold their own version of the BB, and could be a cost effective alternative if you can find them.

Chombi