That can’t be the right Bosch number. The big starter is for the 131 tooth ring gear from 1975 to 1989. Alfa did fo to the small size starter in 1986.Well, I discovered what my mechanic was talking about. Bosch lists one part number for the reman (SR484X) but you dont know if you will get the large bodied starter or the smaller one as fit in my 91. What arrived was the large, much heavier and looks like it requires a support bracket on the other end. So this one is going back.
Your ring gear is 130 tooth starting in 1990. Which is different Bosch number from the earlier starter.
I recommend taking the one in your car to a rebuilder and have them fix it.