a reverse (ie upside down) half leaf on top will help prevent axle tramp - like in the bottom pic in that diagram. bear in mind it will flatten the front part of the leaf a bit and increase spring rate slightly too.

how many other leaves you use underneath depends on what spring rate you want.

I'll see if I can find a pic of my rear leaf pack made from a combo of 1200 and 120Y leaves. it was crude (and ugly!) but very effective.