I found this ad about this turbo and was wondering if it fits my truck ,the ad says that it came from an 8.3L cummins truck he is asking $300 for it. what do you think?

Those are HX40's. They have 21cm exhaust housings and I think a T4 manifold flange, 5.9 uses T3. You can use the compressor part of it and get some benefit.

too big of exhaust housing to be practical.you will need to spend a good amount of money for a different housing and T4 foot adapter. then you will have a turbo that can support 400HP that has a weaker shaft.better to get an s300g for about $1000.