I am drawing the pulley at the moment but to get it light enought is going to be very difficult. As there needs to be alot of material removed to get this the weight needed it would cost alot to machine it doesnt really seem worth it, also if the diff slips with an alloy pulley you will get filings in the diff which will make it destroy itself. Running alloy diff halves should solve the problem as it should dissipate the heat away from the plates better.