I realize that I am answering a question from 2010, but for those of you that are interested...
My dad served on the USS Barb under Adm Eugene Fluckey on the last 5 war patrols (8-12)... So I have picked up some knowledge regarding the Barb over the years... I have also attended several Barb reunions over the years and met many of the officers and enlisted men that served on the Barb along with my dad...
My dad passed away in 2005, but I recently reconnected with one of my dad's friends who is the last surviving officer that served on the Barb, so if I can't answer your questions, I'm sure he can...
On their 12th war patrol the Barb had a Mk 51 Mod 0 launcher and 72 Mk 10 Mod 0 5 inch rockets. They launched a total of 4 rocket assaults and fired a total of 68 rockets...
The rocket launcher was mounted on the foredeck in the area where the 4 inch gun had previously been mounted... I don't know if the launcher was permanently mounted to the deck or brought out and setup for attacks and then stowed away after...
The 1st rocket assault on the town of Shari occurred on 6/22/1945 at 2:34 am. The Barb launched 12 rockets into the center of the town from 4,700 yds offshore...
The 2nd rocket assault on the town of Shikuka occurred on 7/3/1945 at 2:46 am. The Barb launched 12 rockets into the center of town from 4,930 yds offshore...
The 3rd rocket assault on the town of Shoritori occurred on 7/24/1945 at 10:36 pm. The Barb launched a total of 32 rockets. 20 rockets were launched into a factory from 5,250 yds offshore (they fired 12, then reloaded and fired 8 more) and then they repositioned and fired 12 more rockets into the center of town...
The 4th and final rocket assault on the town of Kashiho occurred on 7/25/1945 at 3:10 am. The Barb launched 12 rockets into the center of town from 5,000 yds offshore...
I have never seen any pictures of the Mk 51 mounted on the Barb, though there may be some out there in one of the crew members private collections... There is some video footage of the launcher, but it is very poor quality and taken from up close so you can't get a good look at the launcher... You can view the video on YouTube at this link
https://www.youtube.com/watch?v=wfEzq20EzGU You can see the launcher from 0:15 - 0:26
If you have any questions regarding the Barb, I will be happy to try and find the answer for you.