Scottish steam engines have always had very elegant "faces". For some reason up in the far north of Great Britain, people like to see wings either side of the smokebox. Combined with frame extensions above the footplate and the result is very attractive.
The kit requires only three parts to do this - 2 frame extensions and an extra smokebox front. In 7mm scale this means some pretty big lumps of brass but apart from snipping off a couple of tabs which didn't align as well as I would like with the slots, all go together well.
For fixing I blobbed solder in place using the electric iron. Then loads of flux was slopped around and the solder heated with the small blowtorch. This blows the molten metal along the joint leaving a neat result. I suspect things could be achieved without gas power but it does make the job a lot easier. If the solder is molten all along the joint, capillary action will keep things tidy, as long as you've not piled on tons of the stuff anyway.
Around the top of the smokebox, I just smeared solder between the false front and the existing one with the electric iron. The excess was filed off and polished with some emery paper and a fibreglass stick. As I always tell people, it's not great skill building the model a lot of the time, it's being able to clean up and hide the untidy stuff that makes for a good modeller !