You could make your money back just with the plastics if they are truly 100%.
My comment on the seat was based on the first pic which looks to me like the passenger seat cover was torn off. Must be something laying on it.
I still wouldn't trust the "rebuilt" carbs. They may be fine, but I've seen too many cases of the local bike shop doing a superficial clean up and maybe a bench sync and charging several hundred dollars for their "Rebuild".
My '83 still has second gear and a solid frame and she was beat when I got her. The odometer is around 50k miles now but after tearing the top end down at 30k and seeing that every valve was super tight, I'm thing the odometer was rolled over 100k. If I'm remembering correctly, the 2nd gear thing usually shows up around 60k mi. The frame is going to depend on storage and how much wet weather riding has been done.
All in all, if she starts easy, idles with no "choke", and doesn't bog or back fire WOT, AND the plastics are as good as claimed, I'd seriously consider it. They are one of the best bikes out their in their class.