The way I see it, you should have one isolation movement in your tricep routine because the long head runs across two joints, the shoulder and the elbow. What this means is that, during a press or a dip, the long head will shorten at the elbow, but at the same time lengthen at the shoulder. So for mass, I say include a tricep extension. I prefer overhead db extensions, since the long head is put in the stretched position. For the remaining two heads, I say either close grips or dips.