Please post results on this.
You also need to cut down the mag tube as well. And find a way to bring that mag tube nut detent back to the spot.... or some other retention method for that on/near the rear barrel hanger.
I've seen pictures of super short M4s, but I don't know who / how it's done necessarily. Rose would be where I would start as well, I don't know the shops that have done this for sure - but clearly it's been done there are several such pictures.
The weakness of tube mag fed shotguns when you do this, of course, is that you now have less rounds. I really wanted that 10" setup for along time, but this issue held me back.
Now I have a box mag fed super short SBS for this reason as well.