That was quite early in the models life. I bought my 156 TS 2,0 (1999) in 2002. I got a copy of the invoice (2001) for the last service it had before I bought it which was done by an very reputed Alfa dealer. I could see that it had 10W-60 oil in the engine.
At some later point in my ownership I had the cam seals changed at a cam belt change. The mechanic said that the 10W-60 contained less purifying ingredients than the long life 10W-40. Since then (about 80k miles) I used 10W-40 and changed once a year.
About 10-20% of the 2,0 TS engine had oil consumption, a fair bit of the JTS had had. The 1,6 and 1,8 TSs usually didn't consume any oil.
I don't know about the 3,0 and 3,2 V6s.
My expediences with North engine is that they leaked a bit of oil (from the rear crank seal) unless you use fairly thick oil. I don't remember what I used my Giulietta 2,0 and 75 TS (probably 10W-40), but in my Spider 1750 I used 20W-50 - no leaks and no oil consumption (it didn't do any winter driving). When I bought it 15W-40 in it and it leaked. Next change change it got 20W-50 and no more leaking.