Aluminium is strange stuff to work if you're used to steel, it's taken me a while to get the hang of it. Making something else first, like wheel spacers is a good idea, as it's not such a loss if you mess up and it gives you a chance to get used to working thick aluminium.
I've been re-drawing my the plans for the triples and getting them checked over. I hope to mark them out ready for cutting later this evening.