You can tune anything, I had a 1.6 8v 100bhp engine, exshuast mods inlet mods head mods and came off the rollers at 165bhp. That was mashing together this and that, which no one had done and said it wouldn't work, I drove it hard for 2 years on the road and track and its still been raced now 2 years on and still going strong on standard crank rods and pistons.
My 300tdi feels dangerous having a tweaked pump and turbo landys are not built for speed,
If I were thinking of buying it I'd be hoping that he's spent as much on the brakes as the engine