I don't get it, cosworth made rwd cars so why not just use that box? What car are you trying to fit it in?
Are you thinking yb 2wd in to something else?
I have an mt75 with the front of the bellhousing lopped off if you need it for bits?
My friend has adapter plates to get then RX8 6 speed rear wheel drive box to fit yb, zetec etc...