Some time in the obscure past I acquired some odd 50 pound dies and used them to make top and bottom flat dies on "U" brackets. I figured I would fit other quick-fit custom dies over them with saddle mounts. This has worked fine so far. If I had a long run of some particular thing I would probably remove the bolted flat dies and replace them with other custom bolted dies.
The images show what I cobbled together. The bottom die is a KDS lower base turned upside down.