Hi
Similar to John"s suggestion just a bit different.
If all you want at this stage is that the wheels are not on the flange might I suggest a slightly different approach that I have used. Not sure what gauge or size you need. Not sure how heavy. Here is the method. Whatever the depth of the flange get some strips of metal your 3' long that are just over the depth of the flange and say about 1/2" wide. Screw them down to a board such that they are parallel and to the correct gauge. I typically use 1/2 x 1/4 steel. Now fill the center with 1/4 hardboard leaving a width for the flange. Next on the out side of the "rail" cover the rest of the board wit 1/4 hardboard. You now have a track that you can move the engine back and forth, with the advantage that it cannot drop down through the track and damage anything, it cannot derail and cause damage. Screw down a block at each end for safety.
Took more words to describe, it is fairly simple. I had 1 1/2 scale locomotives and rolling stock that I transported in the back of van, three tracks. With this type of floor and I never had to worry about a locomotive jumping off a track.
Anyway just a different approach, no rail to purchase just material. You can make it out of anything. You can also at some point work in some ball bearings so engine can actually be run when on the rollers.
Bob