http://www.metalreference.com/INFO_Aluminum.html
The difficulty in making the tabs on the sides so you can
use the existing floor plate is NOT bending it past its
"Minimum Bend Radius" and having the right amount of material
other wise it will crack and or break off.
Heating to 650-700° and then cooling in air to 500° is the most basic
method I know of for making it soft for working.
Also Aluminum doesn't change color when heated.
You over heat and it melts. That's why you can't just
apply a torch to it and guesstimate.
I read though you can cover the surface with a layer of Soap
and apply heat until it turns Black and it's hot enough to bend.
I have never tried that but it's interesting.
So what I believe is that when making the tabs there needs to be
a good inch or so of material there, then use a Jig with small pin or Bending Pliers to
make the bend and then trim the excess aluminum off.
When you look at a factory mag you'll notice 2 ( 1 on each side ) notches
in front and back of the tab. There are 4 on a magazine. They have to be there I think
to prevent cracking the body while bending the Tabs for the floor plate.
That's what on my mind and I'm not a professional.