Thanks for posting pictures of your 105 project.
Looks great.
Regarding changing barrels. Look for a manual
on line for the M101 howitzer. It describes
the tools used and a few images of how a barrel
can be changed by several soldiers.
Link for online manual. http://www.scribd.com/doc/13775212/Howitzher-Light-Towed-105mm-m101a1