For what it's worth, it is possible to remove and refit the starter motor from underneath the car, with everything else in place (no need to remove the plenum chamber). You just need a 13mm socket and a couple of medium-length extensions. Obviously, the bolt closest to the engine block, behind the starter motor, is the most difficult. But you can use the fingers of your left hand to guide the socket onto it, if you reach in through the left wheelarch, over the driveshaft, while lying under the car.
In terms of difficulty the Twinspark starter motor is only a 7 out of 10 compared to the starter motor on a V6 (under the exhaust manifold), which is a 9 out of 10.
Just remember to disconnect the battery first (a real sparky surprise if you don't) - and if you take the starter motor apart, mark the solenoid so as to get it on the right way around. It fits easily in the wrong position but half an hour later, the main supply cable won't fit through the plastic terminal cover, and it will all have to come off again. Don't ask how I know this
"If a job's worth doing right, it's worth doing three ****in times", as my friend the Italian car specialist says.