Numbers..aren't matching?

Don't worry about it. In NH, they don't check those things and they wouldn't know to look over the brake booster. They will not issue you a title either, you will only have the bill of sale and registration. If you sell it all you have to do is write a bill of sale with the correct vin# above the booster and when they register it, it will be correct (hopefully it's not stolen). Call the DMV in Concord as anonymous, say you are thinking about purchasing this car, give them the vin# in question and have them run it for you.