Because the original Birmabright mudguards lasted so well, I wanted to use Birmabright for my project bike. Not knowing the modern day equivalent of Birmabright at the time, I ended up with 5052 Aluminium which is a similar alloy. The idea to use 5052 came from a Landrover website. Several members there had been using 5052 for years to do repairs to the Birmabright Landrover bodies. They claimed that the 5052 was an even tougher and more vibration /crack resistant material than the original Birmabright. 5052 is readily available here in North America. It is fairly tough to shape even after annealing, but rewards you with a very sturdy product that does not dent nearly as easily as the more common and softer alloys.
I used it for both mudguards and the seat cowl, but decided it would be too much of a struggle for the petrol tank, that I did in a softer alloy.
Glen