As for as differentials go, I'd trust Cusco over Kaaz. I was chatting with a local tranny builder who builds most of the rally tranny's in my area and he said the Cusco's are better in his opinion. With his experience, I trust what he says.
That said, I had no idea the JDM RA 5-speed had DCCD. Can you modify a USDM WRX tranny to have DCCD too?!?!