G'day Beeno, welcome to the forum, and nice choice of car.
I'm on my third 90, and my first tip would be JOIN THE CLUB. I learnt more in my first month of membership than in the year beforehand trying to work on the car and research on the net.
My second tip would be, read through this forum thoroughly, this is the third time in two weeks I'm about to post this information.....
You won't find a service manual. The only one available is the 15(or so) volume they sent to Alfa dealers at the time. You'll be very lucky to find one of those. That said, occasionally a CD-ROM pops up on Ebay. There is a part manual at this website:-
http://www.geocities.com/MotorCity/Downs/7709/manual.html There's also other good information on the 90 if you navigate through the site.
there is a very good 75 manual here:-
http://www.users.on.net/~craigf/ there are a lot of similarities between the 75 and 90, so what you can't find on the 90, you may find something useful in the 75 manual.
I have a few spare parts lying around, especially since I've started stripping one of them for trackwork, let me know if you need anything, or any information. I had to do a bit of electrical work on mine too to get it roadworthy, I know how it is. I'm guessing the indicator stalk doesn't stay on and/or self-cancel and the headlining sags a bit?
Where did you buy the 90 from by the way? Any pics?
Good luck with it
Sheldon