How do I lower the rear
 

I was reading about how to lower the rx7 and I heard you can't put coilovers on the rear because the strut towers aren't strong enough, what do I use to lower it

Cut springs, trim bump stop, maybe some shorter shocks (depends how much lowering you do). If you lower more than an inch or so it will mess up the front steering with doing something about the bump steer.

That t3 stuff is just a spring over shock coil over that mounts in the stock shock location and that upper mount is not built to take all that force. I wouldn't use em.