There are at least a dozen guys here that have worked on outboards for a living for 30 years. They are the ones I'd want a "review" from. In particular, if I wanted to know about a used motor and it was a mercury, I'd post a question about the motor I was interested in and hope that Laddies answered, for any OMC product I'd hope F-R answered. If it were motors that were just a few years old I'd hope several others answered.
I don't think I've ever seen a site that you describe, but if you find it, post an address---I'd like to see it too!

I once asked about a '56 fastwin I was thinking of buying and was told all about it, even about the lower crank seal that was notorious for going out, and easy to change to the newer style to eliminate the problem. Just a suggestion, ask about it heer---someone will know the motor you're thinking of well, and be able to give you the goods on it.
Later,
JBJ