Yes I would say that is the best way to fix it by riviting and then running silver solder around it and the rivits.
The location of the pad is given on the boiler drawing sheet 9, a bit of calculation and sketching should get the angle about right and the packing shown on sheet 6 will take up any slight error lengthways.
Bracket is not much more than a plate with the lower edge cut to follow the boiler, top suit the lug on thetrunk guide and something pleasing to the eye to join the two. the four holes are best spotted through from the angle and lug on assembly