Welcome to the madness.

I am currently working on a RDB (Rear Disk Brake) set up myself.

You said that you have the 320-6, is that the 323 with the RDB? That is what I am using.

The trailing arms mount up to the existing rear assembly very easily, the only tricky part is taking the rear spring seat and sway bar mount off the old trailing arm and weld it to the proper space on the new trailing arm.

As for the shock mounts, that you can go either two ways
1) Cut off the old shock mount and weld it to the trailing arm near the hub (it is best to have the tailing arm on the rear assembly with the brake caliper attached to determine the shock clearance

or

2) Use the existing hole for the shock mount on the 323 trailing arm, however I don't know if the position of shocks attached would cause clearance issues.

Make sure the parking brakes components are up to snuff, the cables fit right into the existing lever connection, but you will have to trim the tubes for the cable line about half an inch to make the connections

Besides that I would use E30 calipers and rotors (greater availability and bigger pad options) some DOT or custom brake lines and you are done.

There was a guy in Sweden who did this and posted pics, I think it's bmw2002turbo.com

Hope that helps!

J.E.