My recollection is that some of the diesel conversions also had such a coupler (1104? maybe EDIT: nope, not that one) but I don't know if they have a coupler box or utilized the existing one with some sort of modification.
It would be helpful if MTL, in addition to the coupler conversion guide (which is indeed quite useful), would share a "reverse lookup directory" or online "coupler selector" where we could check boxes for underslung, not underslung (and are there any "overslung?), T-shank, length, etc., that would give us the product number for a particular configuration, as opposed to having to search through dozens of options, often with "hazy" descriptions.
EDIT- see link in Maletrain's post below