The machines that use them that way are not very rigid at all.every time I see those v-groove bearings used on a machine, the design use a minimal surface of the bearing itself. People use them on thin edges and that puzzles me.
Ideally, you don't want to use aluminum angle at all. The wheels will constantly wear into the aluminum.
At a minimum, steel angle should be used, but the hardened track that's made for the V groove bearings is the best choice.