I noticed that with 1.5mm thick pulleys there was way too much sideways play on the chain. So I decided to laminate two of the pulleys together (making it 3mm thick). I had to file the tips of the sprocket down but now it meshes with the chain very well. It also gives me twice the gluing area with the bearing so I'm hopeful that this will last.
Ideally I would have liked to make this out of 2.5mm carbon. I haven't had a chance to weigh it yet but it's definitely lighter than the stock pulley. I will ride it for a couple hundred km before making the upper pulley, just to make sure that it holds up.
I also plan on making an inner mech plate. So I will keep this thread updated.
If anyone's interested in the .DXF files just shoot me a PM and I can email them to you.