Prestolite new distributor drive gear fits IBT 4101 S and U , 4301 B C and D .  May fit others.   The original part number 90-597 also included the pin and "top hat" type shim washers.  The pin is included but the "top hat" type shim washers are not. John Deere Reference #'s AT21721 AT21722 AT21351  We do include one 0.010" flat shim in case it's needed.  Some applications that used these distributors are