I ground the flat heads off the rivets with a Dremel then just pushed the remains through with a pin punch.
I replaced them with three flat head M4 screws with nuts, but had to file the heads down about a mil, i shaped some washers for the nut side to lock into the raised edge of the lip on the inside plate then loctiited the nuts, then bent an edge of the washer over the nuts. The abutment ring keeps the clutch thrust washer well clear of the nuts. Nowt rubs but it's all a bit fiddly.
Enjoy
Jase