cam retainer ring needed sor BBC?

[sammy]

hi guys. Sammy here from texarkana.Im usualy a ford guy,BUT Im building a 72 model 454 chev, and havent found the cam retainer that would bolt to the front of the block....is this something that is comonly missing from these engines? I have yet to find one anywhere? there are obvious bolt bosses for one but either mine wasent in it or I have lost it... very confused on this point and could use some engine bulders advise. Thanks guys..Sammy