As far as I know he is measuring it all up and he thinks the standard AP BBK for the 335i will go straight on. If that is the case why bother to make up special parts. If we do need a custom part then I think AP will make it up. The idea is that AP will have a full 135i kit - calipers, discs, pads, hoses and all fittings - I doubt he will want to mix AP parts and custom parts from an unknown source.
However, why not e-mail Kevin Bird and tell him we've been chatting (my name is Jack Leverton) and that you have a proposition for him.
His website is: http://www.birdsauto.com/
Let me know what happens.