I just ordered a brand new Moroso one from salle chevrolet for $100. thats the best price I found on the web. Thats a good deal, you would spend that much on the guts. Summit has them for $190
http://www.moroso.com/catalog/catego...?catcode=41221
its the one without vacuum advance, but you can put one in if you like.
http://www.sallee-chevrolet.com/clearance.html