Though I can't "decifer" the model #, I WILL say that the 90 Yama (3 cylinder, 2-stroke in your case) is said to be one of the BEST "90's" out there!
Info I've seen on here is that they are VERY fuel efficient, as well as a "strong" motor for what it is! I think it's probably been around for a number of years (maybe 15?), too - and still being made!
Have the motor checked out by a CERTIFIED Yama shop just to make sure all is o.k. - compression, carbs, etc.!
Ask about # hours on it - although it's anyone's guess, unless the owner has a LOT of records? Could be 300-500, if "average" use?
I have a 2001 115/2-stroke - Yamaha makes an EXCELLENT motor - just take care of it, as you would ANY motor - car, lawn mower, etc.!
Regards,