The colors look to be 1990-1991 due to the white upper of the hull side, and the font of the freedom on the top. Could be an 89 though, mines an 89 and I recall most of them having sold sides. These boats are actually great little ski boats.
Looks like your in SE Michigan, if he needs OMC parts Michigan Marine Gear is the place. The owner is from the original OMC team, and purchased most of the dead stock when OMC was transitioned. This is the best shop in town for OMC -
http://www.michiganmarinegear.com/ I personally use Art Cook Marine service on Harsens Island for my work, but thats due to proximity, and a personal relationship, but Art knows his ways around OMC stuff as well.
Just look for soft spots on the floor, but it doesn't mean you cant use the boat, and big thing like LouC mentioned is the shift cables, listen for grinding of gears upon shifting, will tell you what type of shape the drive is in. Frankly it might be a great little boat for the price (sounds like you got a deal), and depending on the interior condition all it may need is little elbow grease and some compound it might clean up just right. Double check to see if it was properly winterized. Overall just check the fluid in the drive and make sure everything is aligned and not dry rotted.
Doubtful the trailer will work for him, for the Nautique you really need a trailer with a drop down for the rutter/keel/prop depending on the year. Also the Nautiques have more of a flat bottom, where some of these FW trailers were designed for the deeper V that comes on the I/O boats.
Best of luck,
_________________
Rob

Present: 1999 Formula 280SS
Past: 1989 180 Horizon
http://www.robcamerondesign.com