I had it done by Dennis Waldron at Just Trains 10-12 years ago it, but it’s currently packed away and I can’t get to it easily. I’ll be happy to share pics when it’s found. You are right, 031 are a bit tight-and the S curves of a pair of switches will not work. I should get my dremel out and cut away a little more of the plastic rear assembly. We substituted truck with the coupler attached, and had to improvise a little to keep it centered so it could be used without a human to align it.
dick