Excuse me, but how is gravity different on one exercise compared to another seeing how its a constant 9.8m/s^2??
TESTOSTERONE NATION | Tricep Pulldowns: What Attatchment? - Page 1
A few posts in is a list of tricep exercises categorized into Tricep Head Involvement in particular exercises by a guy named Bill Roberts. They're results of MRI studies done on the tricep by Tesch in the early 90's showing which head was being used on which exercises.
Also two more great exercises not on the list and havent been mention yet are JM presses and "Inhuman" CGBP. The latter involves a smith machine but is surprisingly good and used by a few of DC guys like Justin Harris.