Welcome No_Slack!! *I really like the 18 fisherman. *I was looking for one of these when I found my v20 Steplift. *I'm not entirely positive about the size of the tank on the 1983 18 fisherman, but the 1985 18ft fisherman has a 43 gallon tank.
http://www.wellcraftv20.com/gallery/album15/page3
and the late 80's and early 90's have a 52 gallon tank.
http://www.wellcraftv20.com/gallery/...log_v20_18fish
I also believe that the gelcoat color you are looking for is glacier grey although you might want to try to confirm this with wellcraft.