Like the title states, this would have the threading about 1.5 inches up into the brake, with the bottom part of the brake fitting over the barrel so that it would be able to still be a ballistically superior 11.5" barrel, but have the look of a 607 style 10" barrel.  Does anyone make such a muzzle device?

ETA:  None of the perm-attached stuff.  This is going on an SBR.

You are not trying to hit 16" are you?

No.  GX-5857 lower is an SBR.

No such slip-on moderator existed over 11.5" barrel.

I know it "didn't exist" nor would such a thing be "correct".  

I'm asking if it exists NOW.

This one says it covers 1.5" of the barrel but it's guntec...
https://guntecusa.com/product/ar-15-micro-slip-over-barrel-shroud-with-multi-port-muzzle-brake/

I can't for the life of me remember who makes it but ther is a moderator that goes over the barrel like you want but the barrel has to be turned down a little bit. Also I think the 11.5" might not leave enough barrel in front of the sight post for it to work. I think it goes  2.5" over the barrel?

edit
found it

Perfect!  Thank you!

Now, need to find a place to apply the finish to that one...

Do you have enough barrel in front of the FSB for that one? There are a few places that have slip over moderators like that but they need about 2.3" of barrel or more after the FSB. Reason I had asked about the 16" earlier. I was looking for similar as you few months back. I browsed for a couple nights poking around and never found anything. I did find a couple threads somewhere where someone took one of these slip overs, cut it to proper length, put it on a lay or whatever that machine is and machined it down, then they machined the flats into it. (Basically shortened it) When I built my GX-5857 I could not find a 10" pencil barrel at the time but found longer pencil barrels so I had planned to do what you are doing but never found the right length slip over. I ended up just going with a 10.5" .750 barrel in the end. https://imgur.com/a/JAPq11s

Also, you can buy some Manganese Parkerizing/Phosphating Concentrate, heat it to 200 degrees, drop the part in for about 20 minutes, and you have a proper phosphate coated moderator. https://www.ebay.com/itm/274786699060

I have done a few parts with their stuff and they came out great. Same GX-5857, I cut the lug off, sanded off the flashing, and re-phosphated the FSB - https://imgur.com/a/6uvXtyn

Interesting; thanks.

I guess we'll see if it works, as I've purchased it.

I don't want a 10" barrel because it's horrible for 5.56 stabilization, speed and accuracy.  11.5" is significantly superior in every way...  but I am going after the look of the model 607.