As far as I can tell there appear to be 2 different versions of the gun (not including hero or stunt). There's the one that features in both the poster (above) and the pic chole linked of anderson here
http://i.imgur.com/nCElh.jpg which has a large section at the back that looks like part of the slide, then there's the one featured below from the empire cover that only seems to have the ribbed section as the slide.
I've drawn both up below, and have modded some of the details of the original i did. I think the one I prefer is the bottom version with the smaller slide, I took the new details from the pic above, and took the right side details from the previously mentioned anderson pic and the two sides do not mirror at all as you can see.
So the plan is once i get the details for the right hand side a little more finalised it'll be ready to start building it, once i find gainful employment that is which hopefully will happen by the time the film comes out. I also have the badge and the helmet to do.
As far as the screen, in the trailer there is a closeup of one and it definitely is a working screen, something changes on it very quickly. I imagine this is a non firing bells and whistles version, I have this image in very high def which I plan on altering and simply printing at high quality then fixing into place behind a sheet of plastic. To be honest, full functionality is not a concern for myself personally, as all my stuff is mainly for display and spends 99% of its time in a cabinet.
So stay tuned folks.