An odd model 39 accessory?

[SWTIM255]

I had been looking for one of the old "Japanese model guns" copy of the model 39 for years now. I want to chop one up to build a model of my ASP or Trapper Scorpion.
I found this one on Ebay and bought it, thinking that the wired grip would just be discarded and go from there.
Now that I have it, the whole thing has raised my interest as to what the heck it is.
The grip is a very well made casting from aluminum.
The grip screws are just cast into the grip, it is attached by three screws that are on the inside of the grip
The slide release has been replaced with a well machined pin.
The rear sight replacement has a cast in rear sight, but the front portion is a steel replaceable hook, that actuated ...something...as the slide moved rearward.
I had 1st thought that it was a "Man from UNCLE" style scope mount, but the hook assembly kinnda kills that.
The "mount" part on the grip, shows that something was in and out of it a lot.
Having spent 40 years in every facet of the gun bizz, I can say, there was a lot of money put into this unit, it is not a prototype, or POC, the casting is way to well done.
I can also say, this one has me stumped.
The trail is cold on where it came from, as the person I bought it from had picked it up at a auction in Puyallup, WA, and had no idea what it was.
I think that it ended up on this plastic blowback pistol, as a trade show display.
I had a company that sold these models in the 80's and a lot of them got sold for just that purpose.
Has any of y'all ever seen anything like this?
I do love a good mystery

 

[SWTIM255]

some other pics

 

[Old_Cop]

Maybe a belt mount which rotated the pistol into the firing position without grasping it ?

 

[SWTIM255]

The hole is threaded, and has a raised part that would "lock in" whatever attached to it when it was screwed down, the Bridgeport style holster would be an idea, but the rear sight actuator assembly does not fit into that idea as far as I can see.
My 1st thought was a scope, but again, no need for the RS piece, then I thought maybe laser, but the time frame they would be building this would mean a huge battery package, and it would not fit this size pistol.

I have thought a camera, and the hook tripped the shutter.
I developed and brought to market a gun mounted video camera in the mid oughts, and did a ton of patent searches then, and do not remember seeing this.
The grip has a 1600 grit or so surface, almost like the "Armourhide" that Gerber used on it's 1st mark II knives.
Someone put a lot of time, effort and money into this, during what was a short time period that the single stack 9mms held reign.
This might just have to go into my "what the heck" pile, along with a 22 long rifle, ring trigger, double action, internal magazine fed, open bolt, that even the NRA and BB museum have never seen before.
I guess weird things, find weird people to own them.

 

[SWTIM255]

Well, a person on a facebook group figured it out.
It was a system to convert the Blowback model gun, into a gun that could shoot plastic BB's
predating the gas powered blowback airsoft.
I guess it shows the lengths people will go to, when you ban them from having the "real thing"