I believe Polemidis has the same goal as I do. Strong yet light grapple. Which is why I asked what machine this is going on. I've Ran a Terex loader with a root rake I could push 24" Dia 60' tall trees over with. When that wouldn't do out came the Hitachi excavator. While the rake on the Terex was nearly indestructible it weighs more than my little 2038 deere tractor does. Wouldn't do much good on the deere. My point is build for the machine. You can over build and not leave enough power to get the work done.
I don't know what alloy Vixr1 used but A36 has a 36ksi yield strength. A572 is 50ksi. Ar400 is 155ksi. More than 3 times the strength, Also has better impact an abrasion resistance. Save the weight, buy the better alloy.
Good luck