Thanks, Splint.

I had wondered about steel angle. My worry there was, and is, how much a 3/8” deep kerf in the slab would affect the door’s strength in the vertical plane. The door would only be 1/4” thick under. The kerf (and I’m going to be doing some shallow inlay on the face which will make it even thinner in spots).

I hadn’t considered steel miter bars. The nice thing there (beyond the stiffness you mentioned) is that it’s interchangeable with the T-track. (I haven’t done much with steel. My only real experience with it was with 6-foot long 1” x 1/8” bars, and that stuff flexed a lot. I mounted it on a wall to hold photos with magnets, so the flex was a non-issue. I guess 3/8” thick bar is a totally different animal, especially given how short it is.)

I’m not following your “embedded track being worse than nothing” comment. Are you saying that the screws holding the track to the door backs would loosen, making the track ineffective (and that, being covered, there’d be no way to snug them down)? Or are you saying the track is not stiff enough to have any benefit at all?