I have not, at least not yet, but others have. Here is a website with several interesting projects on a Four Winns 268. There is also a lot of info on what is inside One of the projects is a new A/C install. Here's a link:
http://boat-project.com/sitemap.htm#nav If you are replacing an existing unit you might give some thought to what size (BTUs) the replacement is. The original was 5000BTU. There are some units that are 6000 or 7000 BTU, or you might be able to shoehorn a larger unit into place, but you may need to change the circulation pump, ducting, and other parts. Some others on this site have added another A/C outlet on the front side of the galley cabinet to cool the front of the cabin. You might do a search in the Vista category.