Pepe's done this a lot, I've only done it after cutting fin down and reboxing at a different angle.
If you're going to do a few of them it's worth making a mold. If not you can add fiberglass and bog to get the required shape. You'll need another barrel bolt though, they were hard to find a while ago. I've made my own out of a stainless steel bolt, but it's hard work with stainless.

Or if you can source a scrap board with tuttle box, you can use that as a mold, but be sure to use enough release agent!

PS, be aware there seems to be more than 1 tuttle standard. There's different theories about this, I've heard it's a metric/imperial thing, or there's the real copyright version, then there are those un-copyrighted that are approximately near enough without infringing copyright.