OK I'm a wuss but doing this for my first tig alloy project was a step too far. I watched a few Youtube videos on the process, cut a nice vee with a tiny carbide burr , gave it a really good brushing with a new ss brush and got out my little Mapp/Oxygen torch. At first I was scared of melting the alloy but in fact I had to turn the heat up to get enough heat into the casting. Once I got it hot enough and used a pointed stainless rod to scratch the alloy below the surface things started to work. A bit of a faff and took a bit of practice but the end result is shown below and I'm well chuffed. A very expensive item saved and hopefully I'll be back on the road before too long! In fact I went back and added some more to fill in that hollow on the left.