I owned a 1970 GS455 number matching car from 1998 to 2009. I had sold my '86 GN in 1998 to buy what I thought was my dream car. It was a fun time of ownership but within 6 months after purchase, I was missing my boost fix! Bought another TR in 2000 and kept the GS too.
My advice- if you are seriously looking at one with a vinyl top, look hard as these cars (as most of that period) could develope rust issues with the back glass and top due to the design flaws. They ride good (full frame) but aren't near as practical as a nice Turbo Buick on many levels. I have no seller's remorse on selling my car. I was able to double my investment, but I can tell you that the GS brings way less $ than a comparable SS Chevelle, GTO, or 442 of the same year model. Shouldn't be that way but it is, and that can work in your favor as a buyer as it is a buyer's market in this economy. Roughly 90% of production of the GS were automatics and manual/ stick cars are very rare. Good luck!