high mileage reliability?

hey i had somebody offer me a really good deal on a 95 gs-r. well the car/motor has 307000 miles on it. if i had the valve train rebuilt and the block ie pistons, rings, rods, replaced would it be a reliable engine. its never been raced and its all highway miles. also was planning on sleeving for future turbo. i think it would be just fine but if ya guys think otherwise let me know and ill just get a new engine.