I did up some plates/rails out of some thick aluminum some years ago because the OEM seat track wasn't the same width as the new seat bottom frame and none of the holes aligned. Things slightly changed since then. I'm currently on a manual seat track for the driver which is thing gauge steel, reason being I can weld up some angle iron to preserve the factory sitting height (the aluminum setup raised the seat some millimeters which is actually quite noticeable when driving and I wasn't feeling it).
Like ttocs said, overbuild it. Not something you want coming lose for any reason.