Lower unit interchangeability between years and hp?

[F14AM]

I'm new to outboard motors, but have a little experience helping friends work on them. I've always had inboard/outboard boats. I just bought an 89 Starcraft pontoon with an 89 mercury 60 hp. The motor is good, but lower unit is locked up. From what I gather, in those days, mercury didn't go by year model, but by serial number. I plan on rebuilding the lower unit, but in the mean time, I want to buy a cheap used one so I can take the boat out. The motor serial number is 0C188777. 89 seems to be a hard year to find used lower units, which brings me to my question: what (if any) year/hp of lower unit will fit on my motor? For example I can find plenty of 1987 70hp lower units. Would these bolt up? If not, are there any other years/hp that would fit? It's very frustrating because with other vehicles, you can easily find information that says "this transmission fits 93-97 v8 camaro" or whatever. Any help would be greatly appreciated! By the way, it's a 3 cylinder. Other than that, I can't seem to find much information about it.

 

[faztbullet]

1977-1989 small diameter housing 3 cylinder 60/65/70 unit will fit ..

 

[F14AM]

1977-1989 small diameter housing 3 cylinder 60/65/70 unit will fit ..

Thank you very much! Do you happen to know any good sources where I can find information like that on my own?

 

[faztbullet]

Something like this will work but hes about $ 200 high..
https://sanantonio.craigslist.org/bpo/d/rockport-65-hp-mercury-motor/7145007021.html