[NeilBlanchard]

The rear wheel skirts are not permanent - there will be a rabbet joint on the chassis and the skirt will be attached with either screws or clips and screws.

There is a Saab dealer nearby - maybe a donor 900 can yield the drive shafts (are they close to equal length?) and/or a steering column, or steering wheel (with airbag).

Are there any trailing arm rear suspensions with only a lateral link in the center i.e. no beam axle? Maybe I can get something close to what I need?

The steering arms are almost always behind the king pins, right? And the steering rods have to be straight out to the steering arms, correct? I want to use manual steering, and the steering linkage needs to also push the appropriate front wheel skirts outward when needed, so the steering "stuff" is going to be interesting.