Some years ago I built a unit like you are talking about. As a matter fo fact, I think I sent it away just a few days ago with the junk man. I took a piece of plate some 4x8x3/4 and milled the face flat. Then I used something like 1x1 1/2 flat cold roll and milled a 45 degree bevel on them. I bolted these to the plate. I then mounted all of this in my mill and made a finishing cut so they were parallel. Then I cut two slides the same way and mounted them on a stationary plate.
It took some time but the end result was pretty nice for an old country boy.