I have a 1989 formula 272

Over the weekend I hit something in the water and snapped the skeg off my lower unit...the casing has had some deteriation from electrolysis so its time to replace the lower unit...the problem im having is that everything online says 1992 and newer but that it is able to be modified to fit 1988-1991 I am very mechanical inclined...I just don't know much about bravos as ive always had bravos...just want to make sure when I buy it that it will fit...any help would be great...
Thanks Again Harry

also I believe all the gearing is in the top? so any lower will do?

I don't know if it matters that I have drive reservoirs..do all bavos?

Early 1988's did not use reservoirs, http://www.boatfix.com/merc/Bullet/89/89_12.pdf

This will help with your identification question,
http://www.boatfix.com/merc/Bullet/91/91_20.pdf