1&1/2 inch Square Yale 6 pin padlock identification.

[cowboyup]

Hello,
I'm hoping someone will know what lock series this is. I've done some internet
searches without luck.
This lock as a really cool lock. It has 6 levers and is tensioned by a 7th notch in
the key that pushes the bolt assembly. It looks very similar to the model 50 which
is a 5 lever lock. But the six levers can be seen through the keyway and the key
shows the markings from 6 levers.
They can't be picked using shackle tension; they must be tensioned on the internal
bolt.
Can anyone enlighten me? Possibly with a catalog picture? I'd really appreciate
any input you may have.
Thank you,
Rick