25hp Lower unit question?

Hello, Am new to the forum. I have tried search results and can't find and answer. I have a 1988 SG Yamaha outboard with the precision oil injection. I am looking at several "used" lower units on eBay. Here is my questions?

How interchangable are the Yamaha 25hp lower units? (Will any 80's unit exchange?)
Does the "short gear,long gear,extra-long gear, extra short gear" shaft lengths come into play when exchanging lower units?

Thank you for any help or suggestions you can make. I know this is an older motor , but I am really on a tight budget and new outboard or new lower unit is out of the question, Thanks, Dahnkster

Here are photos of two of the lower units I am looking at.

[boats.net]

It is part number 6L2-45300-02-EK, 1988 to 1993 lower units will work. If your model number is 25ESG then it is a short shaft.

thank you so very much for the info

both ebayers are very vague as to model numbers,year or any specifics. The first one I have pictured only says"80's yamaha 25 or 30 hp lower unit" it is definitely the short shaft model that I am looking for but since I don't know what year, I was reluctant to purchase. I was hoping that any pre 1994 would fit (84-93), but I guess only the years you mentioned are the ones I'll concentrate on now. Thank you for your help.