I had to do some repairs on my B310 mast a couple years ago. I contacted the mast manufacturer, which was not Beneteau, and spoke to their "rigger" who got information from their shop people (welder). They gave me the detail of the material and the specific welding rod specs to pass on to my welder. So, unless your mast/boom is labeled as to the manufacturer, I suggest you contact Catalina. I assume given the HIN, they can tell you who supplied the extrusions. In some cases you will have to do some sleuthing as many of the mast manufacturers from that era have changed hands one or more times but most are still around in one way, shape or form. Good luck with it.