Couple tips with the tris - Although I usually double up on work outs like you are, (Ie: Triceps after chest), I often will just do a FULL arms day, that way you don't pre-fatigue your tri's with chest workouts.
As far as the long head:
Basically anything OVERHEAD is going to blast your long head on the tricep, one of my favorites is:
Attach a rope to a lower cable machine - same machine you do tricep push downs on- and put a incline bench in front of the machine and you can do a cable over-head tricep extension on this. Blast these bitches PAST FAILURE, thats one of the keys with triceps, go past failure, if you aren't squeezing your eyes shut and gritting your teeth while doing your triceps, you aren't hitting them properly. The work out BEGINS when it starts to hurt.
Protect your joints though, keep your arms tight.
Overhead tricep extensions like you're doing, with either dumbell's or EZ-Bar is another good one.
Another One arm Cable Extensions, similar to one arm dumbell extensions, but I get a better pump with these - Have no attachment on the cable, stand sideways, grab the cable put over your head and extend. Do a manageable weight, but go past failure on this one as well.
Implement 2-3 overhead triceps into your tricep workout and you should see some ridiculous results.