Welcome!
A 1986 boat is going to be 95% off the shelf items with a lot of it being mostly discontinued and replaced with newer designs in the last 25 years. The upholstery any shop can fix all that, no big deal. The rub rail again is generic, just google search aluminum rub rail. It runs around $100 per 12ft section. If you need the upper railing on the bow? You can try to call a Four Winns dealer to see if they have any in their inventory collecting dust, but if yours is damaged that might have to be custom fabricated. To be quite honest, the boat would look better with it removed and the holes filled.
All the other little bits and pieces? Attwood should be good company to get most of it. Faria makes a good gauge set for under $200.
If you're going to be remodeling, the basic hull design is not much different then modern boats. Aside from the square windshield, a good interior guy and a little re-design can make that boat look 10 years newer. If you plan on throwing money at this boat I would consider your options, because you can easily pick up a late 90's Horizon RX/RS/180 in the 4-6k range with a much better and easier/cheaper to fix drive system. I just sold my mint condition/upgraded '00 H180 for $6500
http://www.fourwinns.com/past_product/catalogs//1986/Runabouts%20&%20Deck%20Boats/06%20170%20Horizon%20(p6).pdfhttp://www.fourwinns.com/past_product/catalogs//1986/Runabouts%20&%20Deck%20Boats/07%20%20...%20Specs%20(p7).pdf