That 'truck gun' is a Mossberg 500 with an MWG Bullpup stock. Mossberg sued MWG for producing it, so it was dropped. MWG made it, and one for the Rem 870. I don't know if the Rem unit is still available. The barrel on this one is 19 1/2", which I cut and installed Winchokes (same as MB) in. Behind the choke, I ported the barrel. Finish is black Teflon moly. I beefed the stock in a couple of places I felt needed improvement. Red dot Tasco mounts in carry handle rail, which has its own open sites. Flashlight barrelmount is a Ruger MKII (pistol) scope mount unit, which I adapted to the barrel. I added studs, something else MWG neglected to do. LOTS of guys have been interested in this setup, which allows shoulder-firing from 19+" barrel, is a natural for the low assault position, and still gets through doors and hallways with ease. It seems to have become an instant collectors item, and I've been offered ridiculous (at least to me) sums for it. SOMEWHERE, the molds exist, if it wasn't part of the Mossberg settlement that they be destroyed. MWG had a neat product with this, but were throttled with the suit.
The porting array is my usual, shown here again on a Mossberg 590.