I own one, it is a great goose and turkey gun. My Defourny was made in 1948. I have seen a couple of them online in that last 5 years. In my opinion, the quality of these far exceeds other 10 gauge sxs's one comes across(typically Spanish). They have both a crossbolt and a 4th fastener. I also like the checkered triggers.

If the condition is reasonable you should be able to get a little more out of it than $600.