Richard, the broken wheel bolts are easy to remove from the drums.
If you look at the back of the drum you will see some threads sticking out (as long as the bolts have not been cross threaded), and will probably unscrew by hand, if not use pliers or a centre punch to unscrew the sheared off bolt. I would suggest you buy a torque wrench, you should be able to pick one up for about £15, it will come in handy while you rebuild your 500.
Mike
