If there is interest in a point by point account of how I did this job on my 156, I am happy to provide that.
Just to add a bit more detail to what I have said previously:
I did not remove the subframe or driveshafts or dismantle any suspension. Where I depart from the workshop manual is that freeing the steering rack is not necessary either, and doesn't work since it does not move sufficiently to get the alternator out.
But you do need to move the engine/gearbox forward. The rear gearbox to subframe assembly/mounting is removed as per the manual, along with the front exhaust (photo 3). You now have access to free the alternator, plenum chamber mounting etc.
To allow the engine to be moved forward: Disconnect the engine to bulkhead mounting. Disconnect the front nearside engine/gearbox mounting (3 bolts, photo 4 - NOT the centre bolt, you'll strip it trying to get it back in !!). Loosen the front offside mounting centre pin a couple of turns to allow the engine to be rotated forward ( be careful - only this and your ropes/jack holding the engine). It is now easy to move the engine forward a couple of inches. It is not as difficult or scary as it sounds, just make sure everything is safely supported before you get under to extract the alternator.
Do the preparatory freeing of the alternator, removal of plenum mounting bracket, etc before you detatch/loosen the engine mountings, so as to minimise your time under the car in this state. And get the mountings (front and top) reconnected/tightened as soon as you have the alternator in place.
The job is fiddly and uncomfortable, but not that difficult once you have worked these things out.
The exhaust downpipe/flexipipe and catalyst are likely to cause some grief if they have been on for some time. I managed to repair mine which involved cutting out studs and some welding. If you can't do this or don't want to buy new parts, this might be the deciding factor on whether to tackle the job from the bottom.
Last edited by merrison; 28-12-12 at 15:17.