Since the IRC cup is made for the Lightning Stadium and we now know the stock Lightning Stadium cup fits the Flux, it's a safe bet that it will fit.
Problem though is that aluminum isn't very strong when you thin it down, and the cup needs to be quite thin to accept the 8x10 bearing. The issue is further compounded by the
diff shaft wallering out the cup sleeve from the inside until it becomes brittle enough to snap; this has been my experience with a turned down
stock cup. With a steel sleeve this problem doesn't exist. Just my opinion.