What is it you hope to gain? If you have the right mtn cur or plott they shouldn't need any crossing.
With that being said.....one of the best hog dogs I ever owned was 1/2 mtn cur 1/2 redbone. (Accidental breeding) But both parents were also good dogs.
My buddy has a pretty good mt cur and was looking at maybe gettin a plott pup. And if the plott pup turned out to have the qualities that he is looking for (down the road) he said some thing about breeding them. And just havnt seen that cross much or I guess at all. We was just curious what they would look like and hunt like!