I haven't confirmed it myself by actually by trying one of the OPC-478 cables, but multiple websites say they are the same -and- you can find supposedly tested schematics of the OPC-478 and it looks correct. As far as making the the ERW-8, yes, assuming your USB cable has the same color code ( it is a standard but who knows with all the cheap far east cables around ) it should work just fine. I've actually carved up several USB cables for various projects and never found one with a non-standard color code.
Your about to delete comment this, are you sure you want to that?