Degree ring slips in between the blower pulley and the hub and uses the six .375" bolt holes as well as the two inch register to help mount and secure the ring. The ring is only .125" thick so not to mess with blower pulley alignment. There is a step machined in the backside .065" deep so degree ring only spaces the blower pulley out .060".
RBS offers timing pointers for the degree ring as well.
Picture three and four show a timing cover, crank hub with degree ring and timing pointer. All parts sold separate and for picture purposes only.