I checked into flywheels and the magneto flywheel on the IT465 has the exact same part number. And by that I guess it has the exact same weight. The crankshaft is another story. The IT465 crankshaft looks a lot heavier, and the IT490 crankshaft looks even heavier yet. The YZ465 crankshaft looks to be the same size, But it has more and larger hole machined out of it, to reduce weight. The motor runs now, so I'm not going to pull it apart just to change the crankshaft. Might be something to try on my spare YZ490 motor though.