I saved the picture and enlarged the gun up a bit so we can get a better look.





It's the standard gun, it almost looks as if the stock of the gun is missing (broken off). The light brown area where the stock should be looks like the cape that is on the cover of the box. Also notice the color of the handle, the gun in the auction is brown and the ROTJ Version is black plus the difference in the barrels and the placement of the scope. There's no doubt in my mind that is a standard gun.

Here are some pics from Kubism for reference on the gun.

Standard Boba Fett Guns (green gauntlets).





Boba Fett Chase ROTJ Version (red gauntlets).



Boba Fett Prototype Version (red/yellow gauntlets).



Box Cover Art.