I just bought a '00 300ex with a '03 gsxr 600 swap. It is a pretty poorly built machine, so I still haven't decided if I want to rebuild it and do it right or just sell it as-is. It is fast, yet unsafe and unreliable right now.
Pros: Frame is already setup for the engine.
Runs but the transmission only has 3 functioning gears.
Will go at or around 100mph with only 3 gears.
Has a Durablue axle.

Cons: Frame is not well built.
Motor mounts are solid.
Rear brake rotor is warped.
Rear brake reservoir leaks (must have hit the slip-on at one point and melted the corner).
4th 5th and 6th gears do not function.
One tie rod is very worn.
One of the hubs is warped very bad, needs to be replaced.

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Scaled it... 462lbs.