Was it the OEM sprocket that you reversed, or an aftermarket? Regardless, if you'd like to play it on the safe side. call up a automotive machine shop, and see if the can sell you a valve spring shim in either .015, or .030 thickness. Based upon your description of how the chain is now nowhere near the case, and the fact that even with the Fastway spacer the chain still lightly touches, from what I've understood, I'd probably think about flipping the sprocket back to the correct side out, and try the shim method.