Nathan,
There are a number of things to worry about when building a generator. First how big is the engine you want to salvage. How much generator will it pull? How are you going to attach the engine to the generator? How are you going to balance it, couple it, keep it cool. mount the gas tank for vibrations, leakage, etc.? These are just a few I would suspect you need to worry about if you are putting this on the street as a mobile power plant. I do not know what you think you can sell your tractor for or how much more you are willing to put into the generator to buy it to attach to it. Harbor Freight has a nice 7KW generator for about $600. I forget the brand name on the engine, but my neighbor who owns a small engine repair shop told me that the engine is the same engine Honda uses on their generator if that means anything. I last fall I adopted the same engine to my 50 year old tractor (I know I should have made it electric, but that is another story) and it has worked good all winter plowing snow. With a new generator set all you have to do is put gas in it, attach a battery and turn the key and you have power. Then all you have to do is mount it to a trailer. If your engine is at lease 16 or 20 honest horse power they also have a 10KW generator for about $300. Again you still have to worry about all the items I mentioned above. I don't have much time for these projects right now, but I am cheap and my time is worth something. I would go with the the 7KW neat, clean and ready to go.
That's my $0.50 worth.
Chuck
