The ally runners will wear, with steel bearings rolling on them, depending on how hard you use the machine. They will also harden a bit when they settle in.
If I was committed to using angle, I'd go for steel angle and spend a bit of time getting it straight.
Personally though, I'd go for steel pipe in replacement of ally angle, like on the early solsylva designs (Bearing Trials~Solsylva CNC Plans )

This is one of the reasons I suggested you post photo's, so we can see how far you have got with your build already.

Richard