Call American Marine:
http://www.americanmarine.com. I ordered the original window spline for my 77 Seafari about a year ago from Mike...he's very helpfull. They made the orginal windows for this boat and still stock the spline. I found this out thanks to this web site and it saved me a lot of time and money. They are a factory fit and will make a big cosmetic upgrade as well as a nice water seal. Good luck!