The answer to your question is not as straight forward as it may seem.
The E21 has a bigger master cylinder and bigger drums, so in effect, a stronger brake.
But it is designed to work with the E21 master which pumps more fluid to the rear.
So it's a question of proportioning the front to the rear. If you use a 2002 master, you will obviously send less brake fluid to the rear, to a "stronger" brake drum. If you have a tii, the rear wheel cylinder is bigger than a standard 2002 but still smaller that an E21. And you decide to go with an E21 master, you have a new problem. E21s have single lines to the front brakes. 2002s have 2 lines up front on each side.
On its own, I don't recommend it. 2002s do not need more braking in the back.
I have "heard" than an E21 rear setup works well with an E12 master and tii front brakes. An E12 has the same calipers up front as the tii but they have rear discs. It's just a rumor but I am doing it to my 69 as we speak. Tii struts, E12 vented calipers, E21 vented rotors and early E21 hubs, E12 master and E21 rear drums.