I bought a bunch of 3/4" x 3/8" steel (MSC) for runners. Thinking about it the Al would help lighten things up a tad 😀
Great thing about the dual runners is you can fix one runner in place and square, then the other can be attached with some sideways adjustment to fit up against the inside edge of the other miter slot. Gives the ability to tune the action and still have the full face to face contact with the miter slot.
To really slicker up the action, the drawer glide tape (HDPE?) applied to the side of the runners really helps, but you need to be careful when laying the sled onto the table to avoid peeling it off. The tape also really does wonders when you apply a bunch of strips to the base of the sled to let it "float" above the table. Slicker that Pomade on a greased pig.