I don't really understand all the geometry that you are talking about except that there is a problem with the breech block fouling the ejector when the cocking handle is rotated uo and forwards into the safety slot. Is this correct? Bear in mind that I am not familiar with the single shot conversions too!

If this is the case, and it is a small amount of metal that fouls, then why not just leave the casing and ejector full size and unaltered - as it is - And simply machine away a small section from the front/side face of the breech block where it is fouling the ejector. The part that is fouling will be the radius of the outer forward edge and nothing to do with the important feed horns.

Or am I missing something in the telling here?