If that's the case it should read 6061 T651. 6061=grade, T6 hardened basically. That's pretty much all we use at work (6061 is tooling grade). Not the best stuff in the world to weld apparently, but having said that my mate never has any trouble with it on all the stuff i get him to weld up out of it. :)
I can't wait to see what you come up with. Nice to see someone doing their own thing their own way.