Howdy
Frigate,
You said earlier....."
...Gents,
Especially Tread.......anyone have some really good info on the LCM's ?... "
Here's some quick, and hopefully useful information on the LCM's
Here is a pic of a WWII vintage LCM (3)

And here are the stats for the above configuration of the early LCM (3)
Displacement: 26 tons; (52 tons, loaded)
Length: 50'
Beam: 14'1"
Draft: 3' forward, 4' aft
Speed: 8 knots
Armament: 2 .50-caliber mg
Complement: 4 crew; 60 troops, or 1 30 ton tank, or 30 tons of cargo
(2) 110-225 hp. Diesels engines; twin screws
Now, on to the LCM (6). This craft was the original LCM (3) hull that was lengthend by approx. 6 linear feet. The added section was almost exactly amidships and fairly easy to see in the photograph below by the darker, unpainted section in the middle of the craft.

The statistics for the larger and more powerful LCM (6) configuration are as follows:
Powerplant:
Version 1) 2 Detroit 6-71 Diesel engines, twin shaft, 348 horsepower
Version 2) 2 Detroit 8V-71 Diesel engines, twin shaft, 460 horsepower
Length: 56.2 feet (17.1 meters)
Beam: 14 feet (4.3 meters)
Displacement: 64 tons (65 metric tons)
Max Speed: 9 knots (10.3 mph, 16.6 kmph)
Max Range: 130 miles at 9 knots
Military Lift: 34 tons (34.6 metric tons) or 80 troops
Crew: 5
Finally, there is the LCM (8), which was still essentially the LCM (3), only this time lengthened even more to a total of 8 linear feet amidships. The engines were more powerful, and there was also the addition of port and starboard floatation 'blister' extensions. Hence the increase in Beam, and Displacement.
The stats for this vessel are as follows:
Powerplant:
2 Detroit 12V-71 Diesel engines, twin shaft, 680 horsepower sustained, Kort nozzles
Length: 73.7 feet (22.5 meters)
Beam: 21 feet (6.4 meters)
Displacement: 105 tons (107 metric tons)
Max Speed: 12 knots (13.8 mph, 22.2 kmph)
Max Range: 190 miles at 9 knots (full load)
Military Lift: 1 M48 or 1 M60 tank or 200 troops
Crew: 4
Hope all of the above is of some help.....
Tread.