No Monthly Fee Debit Card
Leave a little. The step or ledge can be left. Avoid cutting the surface which will fit against a Sigma SA bayonet mount plate. Actually there has to be a spacer between the OM and SA plates, too. The OM focal plane is 2mm behind SA, so shim to bring the SA surface 2mm out toward the camera body. This is not the same as adding a 2mm spacer. 2mm includes the SA plate and a spacer.