you can put in pretty much any Nintendo Vs. game in there easily. You just need the ROM chips (which some members here can burn for you no problem) and the correct PPU (which has to be original).
Check out www.johnsarcade.com to get more information on what games work with what PPUs.
As far as the gun, you will need to find a working gun and the appropriate gun harnesses (there will be two) and then yes, you can play the gun games Hogans Alley, Gumshoe, Duck Hunt, or Freedom Force (I think those are all of the Vs. Gun games).
I currently have a Vs. cab with Hogans alley installed.
Isn't there a minor board mod that has to be done in order for the gun games to work on a Vs. PCB? I can't remember but I was thinking it had something to do with adding a capacitor.
Isn't there a minor board mod that has to be done in order for the gun games to work on a Vs. PCB? I can't remember but I was thinking it had something to do with adding a capacitor.