X, I fear my posts are generally becoming negative!
Never-the-less, things are what they are.
Aluminum is NOT a good choice for frame material because it shall crack from fatigue.
It's only a matter of WHEN that will occur.
From time to time there are MSM articles about spectacular structural failures in aircraft.
If you still wish to proceed on your project it would be advantageous to have a reasonable supply of stock on hand to select from, and a tig welder.
Good luck!
With a bit of work you could have a really kool liteweight racer!
rc