Principal Financial 401k

Up until now my employer has defaulted my 401k into Nuveen Lifecycle Index 2055 Class J. I'm 34, maxing my 401k contribution each year as well. I want to take 40% of my current allocation (~$275,000) and put it into FXAIX. So the allocation would then be 60% Nuveen/40% FXAIX. I also have individual retirement accounts in addition to my brokerage account where I am pretty growth focused already. Curious if 60/40 is a safe way to play it?