Alright here it is, sorry for the delay:
On the left:
Standard Alu control arm, when you press out the ball joint, a bearing cage needs to be installed using circlips to holy her in place. The spherical bearing is pressed into that and also held in place by circlips. A tapered pin is bolted into the tapered ball joint hole on the knuckle. Conical spacers are used to space the spherical bearing down from the control arm for proper alignment.
On the right:
Much simpler although heavier. Typical XI control arm. It is usable on all rwd 3 series. The ball joint end in the control arm is cut off and a receptacle for the spherical bearing is welded and braced in place. The spherical is either pressed into the receptacle or a spherical adapter is pressed in. Using the taper pin again with the conical spacers, you can then space the spherical down from the knuckle for proper control arm angle.
Pretty simple to do, isn't expensive or very time consuming, it just isn't in demand, hence the extravagant price of the kits that are sold.
I just picked this up today:
I ha e a spare set of Alu control arms now so I will be pressing the ball jojnt out and fabbing up a custom kit for my 323. I will also be fabbing up a set of rear upper control arm spherical bearing cages for peace of mind.