8 3/4 gasket locations

The metal gasket goes between the axle housing and the backing plate. The foam gasket goes between the backing plate and the axle retainer.

So installation would go-

metal gasket against the axle housing
backing plate
foam gasket
axle w/ axle retainer

The metal gasket seals the backing plate to the housing. The foam gasket seals dirt out of the axle bearings and grease out of the brakes.

The green bearings should still have the metal gasket between the axle housing and the backing plate, as that doesn't change. But there's usually a paper gasket instead of the foam one for the axle retainer plate. But they're sealed anyway, and there should be an O-ring on the bearing in addition to being sealed. You don't actually have to run the outer axle seal (in the housing tube) if you're running green bearings, and aftermarket axle flanges don't actually leave room for that seal.