Hey Spaced Invader,
Currently, I don't have pictures of my cab, but I will after I decide on a name for it. It is an Alien3: The Gun by Sega. You can check out a pic on KLOV's site. Except mine is all black (except for the guns that are gray, and the gun's bases that are white). I haven't changed the cabinet on the outside, but I did have to make a mount inside for the NEC 27" VGA (rez up to 800x600)--has two S-Video inputs (I have a 3rd party PS2 S-Video cable w/GunCon support). I took out the original monitor that was facing up and reflected by a mirror--I'm not sure if you know about these older positional gun game cabs, but most of them had this mirrored image setup. Unfortunately, consoles don't support this reflection (and some Mame games don't either).
If you check out the picture of the cab, you'll notice that there are two doors to the left & right of the coin door. Anyways, I gutted all the original Alien3 parts and placed my PS2 into one of the openings, and the lightguns inside the other opening. I also gutted the coin door insides and placed my Dreamcast behind it. Below that (where the coins would drop), there is an compartment I use for storing my DC, PS and PS2 games. Other mods I'd like to do are to install 2 holsters and make a new marquee and sideart for it.
As for installing a joystick & buttons--I thought of that too. But unfortunately for me, there is not much space left over on my control panel. I thought of interchangable panels, but the guns are very heavy (much more than T2 ones). Assuming that you don't have positional guns, there should be no problem installing a PS2 joystick into it, and still have room for holsters or openings in the cp for lightguns (or the guns can go to the sides or front--not necessarily on the cp). You can have a joystick and lightgun plugged in at the same time (unless you want to play w/two players--then you'd have to swap). Also, the PS2 joystick is good even if you want to use a PC w/it in the future because you can use a USB-Playstation adapter (I do). I also have the Playstation to DC, Gamecube and XBOX adapters. BTW, I forgot to mention that some of the Playstation lightgun games are NOT compatible with the GunCon (and all are not w/the GunCon2). I have a couple of guns that support each type.
Good luck with your project-I'm sure it'll be well worth your effort.