Sounds like you have a lot to think about. CNG is not going to get any easier to find. Is maintaining your current centerboard so much hassle that you’re willing to spend upwards of $2000 (US) on a stainless steel one? These guys https://metalsnet.com/stainless-steel/316-stainless/316-stainless-plate/?gclid=CjwKCAiAu8SABhAxEiwAsodSZPJ8r-g3u00refQI9ZLAAbVVk7fC30uP1OUj0JwFLvGhHTiNEpvXUhoCY3MQAvD_BwE have half-inch 316 SS sheets 2’x4’ for about $1800. Then you have to have it shaped… Friends who had a Bristol 35.5 – very similar to your boat – didn’t bother with the centerboard and simply sailed with it up. After you’ve spent all this time and money refurbishing, your boat will be worth about $0.02 more than it was before you started. Don’t forget that the reason to have a sailboat is to go sailing!