70ish GS convert

[DM69SS]

There is a house near me with a Buick GS convert sitting outside. I noticed it about a month ago when it was snowcovered and just cringed. I've been busy with a wedding/honeymoon and just got back. Now the snow is gone and I went by for another look. It has collector plates on it and looks to be in pretty good shape. No major rust, a few small areas of primer, but the paint that is there is in good shape and the white top looks good as well. It definitly hasn't sat out in the snow for long. Anyway - I have no idea if it would be for sale, but before I go up to the door, I'd like to know what to look for. I know about chevy's, not Buicks. What should I look for to verify that it is indeed a GS? Also, where is the engine stamped? What is the price range for these cars?
Thanks

[Stefano]

The VIN of the '70 will tell you if it was a 455 car. Series 46 (third and forth number on the Vin). The vin will not designate a Stage One, until 1972.