Yep, it should be fine! If they're double factor, and if yellowface II is double factor, about half the chicks should be yellowface and the others will be goldenface, I think. Not sure, but if you breed sf yf II with df yellowface, then most of the chicks will be goldenface sf? Some will be df, right?
Okay, I'll just admit that df and sf mutations are hard to predict! Someone correct me if I'm wrong