Yet Another E30 Project Car---Unlike Any Other E30 Project Car-The E30 M-Touring. Part 1: Suspension
The E30 M3 Suspension is justifiably famous. Five bolt wheels and hubs with bigger wheel bearings are stronger and more durable than those of lesser E30s. Optional aluminum lower control arms are lighter. Offset lower control arm bushings allow more positive caster for greater high-speed stability and a bit more tire clearance. M3 springs lower the car about an inch; larger sway bars allow flatter cornering. All working together, these race-bred suspension parts turn an everyday grocery getter 3-series into a true SPORTS SEDAN.
Here's the short version of how to do it all at once: find an E30 M3 parts car. Take its suspension out from under it. Take your stock suspension out and throw it away. Bolt on the M3 stuff. That's all there is to it. That's what we did. Here are the details.
Front Suspension:
The M3 front sway bar is larger than that of other E30s giving less body roll when cornering. It also attaches with a link out at the strut, instead of at the lower control arm. This gives the suspension more leverage to act on the sway bar, but conversely allows the sway bar to act directly on the suspension movement instead of to a reduced degree. The M3 sway bar bolts directly onto other E30 cars, but the outboard link can only attach to an M3 strut. We already had Bilstein sport shocks, so these were transferred to the M3 struts prior to installation. 
We used the M3 springs, which were designed to lower the car about an inch. The M3 strut/spindle assembly uses larger wheel bearings and 5-bolt wheels.
Most E30 M3s came with lower control arms made of steel---no different than those on other E30s-but your local friendly parts department has the optional
lightweight aluminum M3 arms that you really should have. The lower control arm bushings are indeed special. They are offset bushings that press on in the usual way, giving slightly more positive caster to increase high-speed stability. These can be installed on any E30.
Rear Suspension:
The M3 rear sway bar is larger than other normal E30 cars, but turned out to be the same size as the rear bar in the wagon. No change was needed.
We transferred the complete rear subframe assembly from the M3 in order to get the larger wheel bearings and 5-bolt hubs [as well as the brakes---more later], but no major suspension improvements come from this change. The M3 rear springs were used and the Bilstein shocks were retained.
So how does it all work? It works great, of course. BMW designed it to work great!!