The SL400 Mags will work with Arri III's, 435's and 235's. On a 435 they sit at a slight downward angle, but still do their job of keeping film displacement weight from affecting the balance of a steadicam rig.
Very versatile mags, and lighter than Arri's own 435 steadicam mags at 1.5 KG! They will run 130fps forward only. They are made of magnesium. These mags alone are $4250 US new each! They are light-tight and very clean - I have never had film scratched. Never have needed to tape the mags in even bright sun.
I have had these mags overhauled by the manufacturer (SL Cine) a couple of years ago (they have hardly been used since) to all the newest parts internally. Here is SL Cine's web page about these mags:
Included is a new custom made flight case (made by Engineered Cade Manufacturing in Toronto) that securely holds all three magazines.
If you would like more photos or information, please contact me.