I mean it's got a stock fairing and all, but has the frame changed?  The engine?  What else is different from say an 01?

Fairing and Oil Cooler. That's all I know and I think that is all that is different.

The engine has an oil cooler added.

Besides the black frame; forks, brake calipers, foot controls, and other odds and ends are sourced from different suppliers (spanish?) but are structurally/performance wise the same.

Are all the holes the same size and in the same spot?  Can I put the tail body parts from a 99 500E on an 04 500F?  Yeah I know that it would look funny, but a can of paint can work wonders.

You could get a new tank and tail and fit it to your old frame with some work.

The '01+ tank and seat/tail are different and aren't really compatable with the old parts. So you couldn't mix them very well.

Whats the difference? about three hundred quid I think..........