Check out this site. It has three-view drawings of all the different boats used. Great site.
http://www.rivervet.com/boats.htm
As far as the LCM3 to an LCM6, LCM 6 was 6 feet longer in the cargo area. I plan on stretching my LCM3 to a LCM6 by adding about 2 inches.
The below photos (center photo) show an actual LCM6 converted from a LCM3. New 6' section is still unpainted.
I plan on building a Monitor and ATC(H) out of the stretched Trumpeter LCM3.
Gino P. Quintiliani - Field Artillery - The KING of BATTLE!!!
Check out my Gallery: https://app.photobucket.com/u/HeavyArty
"People sleep peaceably in their beds at night only because rough men stand ready to do violence on their behalf." -- George Orwell