Apparently you have not worked around interurban equipment with a swiveling coupler. The amount of metal that would have to be removed and reworked on that locomotive is incredible. You would need to find or build a strong and secure enough mounting point for such a coupler clear the swing area, etc. etc.
If you look at some of the posted photos of other 44 ton narrow gauge switchers the trucks and coupler pockets are one casting in the same, thus allowing the swing needed for tight curves. The front/fixed mounting along with the short centered wheelbase of the 21 looks like a receipe for disaster with the lateral forces that will exist on the grades and curves of the Loop. Hats off to the well edjucated people of the Hysterical Society!