For $300, I'd give it a shot. Even if it dies in a year, it's still not a bad deal assuming you reuse your existing TB/WP. You will probably need a new WP gasket though.
For $300, if you don't use it, you can always sell it and at least get your money back (probably make money). Since it's still in the truck and the guy says it runs, I'd definitely listen to it, rev it up and make sure it doesn't have any weird knocks or ticks (besides the normal Toyota "sewing machine" sound that the engine makes). I'd make sure that price includes him pulling it out of his truck too.