8MM retainers/locks on 5/16 valves: OK or not OK?

Yeah there is only several thou diff. these are 5/16 valves for sure (miking at .311"). the Lunati 8MM retainers/locks "appeared" to fit nice & I wouldn't have noticed any potential issue at all till I set the 8MM lash caps on em during my last mockup before final cleaning (& not sure I was even gonna use em after Mike at B3 raceing said not to) but the stud chebby roller rockers are too close to the ex side edge & I wanted to solve that if I could without some special $400 rockers then I saw all the play & knew there was a problem somewhere. EDIT hyd cam/6200 RPM/30 minute feature duration races. MORE EDIT I saw the CC retainers in the speedway add where they say it fits em both, just need diff locks as you said.