Compare the two mags, almost identical, except for three things, the two bloody great tabs at the back of the Savage mag, the friction tab/lock on the back of the M12 mag, and the rib on the front of the Savage mag.
In all Aussie technicality, I set up a small vise on the verandah, dodgy no name dremel tool, a grind stone, some small files and a drum sander attachment. I used leather from an old rifle sling to cushion the sides of the mag to prevent tool marks.
I started by basically grinding the Fark out of it, no bones there, had to take of about 2.5mm of metal to make the same profile as the Bibby mag. Now this is a point that I figured out later, in the Lithy, it must be as accurate as possible, to allow a fit. Anyway, after grinding, I then filed the sides and sanded the rib back until smooth and fit was maintained.
Repeat the other side.
Now the test fit. First try made me realise the fine tolerances of the back of the mag-mag well relationship. This is where the sanding wheel touched it up until just right. All up took about 20mins from start to finish. I discovered that the front rib makes for an even firmer fit than the Bibby mag, and the locating notch at the rear is not necessary for my rifle.
Final fit and test of function, using, of course, Sportco 'Aussie Ammo' bought from BigW (in the eighties) for $2.15 a pack.
So there you have it, a cheap and relatively easy replacement mag for the Lithy 12.
Well done mate, real Aussie ingenuity there. 
