If you go to the link Taigh posted earlier you can see many of the different variations of turret trucks used at the Gunnery Schools. I forgot Las Vegas when I listed the other schools, and it seems that the truck Taigh is restoring was assigned there. I have not found my references that showed a few more turret trainers, but the B-17 chin turret was also mounted on these trucks for training.
Here are a couple of photos of what we have at our Air Base Historical Society storage area:
These are Martin upper turret mounting rings used at the stationary range at McCook Army Air Field when the B-24 Second and Third Phase program was in operation. The crew training fields generally didn't have the trucks but rather used fixed turrets at the shooting ranges. These were tossed in the salvage pile after converting to the B-29 in late '44.
These are the pulleys for the targets on the Poorman Range at Harvard AAF, Nebraska. The pulleys were mounted on poles, cables ran from pulley to pulley, and the targets hung from the cables, just like the shooting gallery at the county fair. The Poorman Gunnery Ranges were used to "polish" the training of CFC gunners at the Nebraska and Kansas B-29 stations prior to heading overseas.
While we're on the subject of Harvard, here is a gunnery training truck used when the 501st Bomb Group (VH) was training there. The CFC system was eliminated on their B-29B aircraft, and the scanners were taught flexible gunnery with this set-up.
Scott