Tony, grafting might work for winterized trees, but here in TX, I wouldn't even bother grafting anything onto a Black Madeira whatever it is. It is easily damaged in winter in TX if left outside. All my UCD Black Madeira growth this season is new growth from the ground up, so anything above the soil including grafts from previous years would've been caput.
IMO this variety needs a long hot season to ripen its fruit.
Perhaps the buyers of those seedlings are conducting research into miracle fruits, and if enough trees are sold, we might get a winner:)