Sure, they exist. Yes, you could put one on a rifle if you have all of the other stuff to go with 'em.

Here's one with close-coupled DST. Being sold by the family of Ken Pointer (may he RIP), who passed away last month. A great guy and the rifle is a real shooter. Also, MVA sells all the parts for converting your LW or HW to DSTs, including the lower tang, if needed.

If you want to see one, look no further than the back of the dust jacket of Campbell's first book. Old Win and I knew this was the place to check. 

Hi all:
Regarding the Low Wall set triggers, the 1998/ 52nd Annual Edition of the Gun Digest has an article about Low Walls.  The author is John Campbell.
He tells us that "The handful of Low Wall Schuetzens that do exist are usually made up on early paneled-side receivers, because the typical wide-spaced Schuetzen double-set triggers mate with this frame without alteration. Factory special orders excepted, this trigger and the close coupled double-set trigger were never offered as standard options on the Low Wall, especially the late version."
On page 9, he shows the beautiful Low Wall owned by Gary Quinlan.
So far as he knows, only one Low Wall factory-fitted with the close-coupled double-set trigger exists. It is a Plain Sporting Rifle, No. 66413, chambered for the 25-20 WCF.
By the way, I didn't know that Winchester never officially called their 1885 single shots Low Walls or High Walls. The Low Wall was called the No. 2 frame, and that was only for the factory's internal reference.
If anyone can find this issue of gun digest, the article is quite interesting.
I hope my post wasn't too long.

   Bill.