When you say tang, I’m a bit confused because I don’t know if there is a technical term for the thick plates welded to the mast usually in pairs and welded 90 degrees to the mast length...but let’s call them tangs. I thought the
photo showed the Vang.
If your welder does not want to grind out the weld and reweld...he’s probably seeing something in the old weld that indicated a weld not structure problem.
When you weld thick 1/2” to thin 3/16 or even 1/4”. It takes a lot of skill and with aluminum, everything has to be super clean. Sometimes the weak area is limited to the
core of the weld and probably the mast will be fine. Cut, then grind. Keep the heat to a minimum. Because you are on the track side of the mast, there is a lot more metal. I very much doubt yo need an internal so eeve.
Neither do you need an extrusion. A good shop can bend you up an overlay piece or exterior second mast wall. 1/4” ought to equal or be larger than your spar thickness. They can bench TIG it so the welding is perfect. Rivet it to the mast and you will have a very strong attachment.
You do not need or want stainless. Pacific Spars used stainless for spreader bases on large spars...they look nice but you can’t see under them to inspect the aluminum extrusion.
You can read a lengthy discussion on the
boat design web when I asked for comments on the best way to close off old
halyard exit slots which are on the mast side. You might not even have a hole and it would be on the strong side.
Fab it up, rivet it on and you will have better than new because the forces are now spread out. Not to worry, it will outlast us both.
Happy trails to you.
Captain Mark and his TIG happy manatees