Have you done all the maintenance to bring the engine up to normal operation? Compression test? Horsepower freak show would require forged internals, and quite a few other parts. 250 to 300 is easily attainable on a budget once maintenance is done. 90+ manifold, bigger injectors, bigger Volvo turbo (15g or 16t), and a chipped ecu. That will net close to 300, but again maintenance first above all else. The gremlins tend to rear their heads if not tended to.