Hi, my friend has a -03 501, with -04 two piece clutch cover.
It's a factory buildt/tuned bike previously owned by Björne Karlsson.
From what I can tell theres no special mods to the inside or outside of the cover or enginecase, exept its a -04 clutch basket.
So my guess is that it should fit.
Edit: Yes you are correct Fry. My friend probably has the -04 enginecase.
My -02 501 just has a little tab there, but i still think it should fit, and yes go whith the -05 cover for easier oilfilling.
Cheers
/Erik