Sorry in advance, your not going to like my reply.
Really, really, really, bad idea!
The shock load on the front of your tractor/ blade/ mount and you will cause some serious damage to one or the other!
Front blades are almost always spring loaded to overcome the shock load.
Secondly your design does not allow for any side to side or up and down float, and because the blade will not float it will dig into everything you run into even the smallest depression or bump.
The blade being fixed will even cause it to lift the front axle on any point that the ground rises up.
Also the size of your materials are going to fold up and bend in nothing flat, three point arms are much heavier on even your little BX.
Your also putting a ton of weight way out front on it, that alone is really hard on you front axle.
Just raise it up and drive around for ten minutes, I would almost guarantee you that your going to bend that arms down, that's a lot of leverage on the arms.
How are you going to feel if you end up eating the dash or steering wheel?
How are you going to feel when the mount breaks and goes through the front of your tractor?
How are you going to react when you've got little or no control of the tractor and blade?
This is all based on first hand experience.
I have the same setup 4 times heavier for the front of my Bobcat skid steer, it has way too many issues!
In one winter I broke way too many parts, and did way too much damage to the blade.
I'll be using a spring loaded plow blade next year!