Just a little speculation about the groove: It may be that if the pulley is transporting something like mag tape this groove is necessary to keep an air bubble from forming and "flying" the tape.
It would not be difficult to round out the bottom of an existing pulley with a lathe-like setup. I save old drill bits to make special tools for that sort of thing.
John Ferrell W8CCW Beware of the dopeler effect (pronounced dope-ler). That's where bad ideas seem good if they come at you fast enough.