KJ = 2x4 version of the Liberty
LJ = 4x4 version of the Liberty
I'm not sure how the 4x4 versions came to be called KJ's also, but that's apparently what happened.
JEEP IDENTITY - Ever wonder what the XJ, TJ or ZJ stands for when people mention Jeep. Well think no more. The letters generally aren't anything more than a way to designate the vehicle with a code. Note that some prototypes may be missing and the dates may be off by a few production years on some models.
MA: In 1941 this was the first prototype in the development of the Jeep. The M indicates a military vehicle and the A the first model.
MB: This is the standard WWII military Jeep built from 1942-1945. The B indicated the second model of the series. (Just a note the Ford versions of the same Jeep were called the GPW. G for government, P for 80 inch wheel base and W for Willys.
CJ-2: The first of the civilian model Jeeps. CJ stands for Civilian Jeep built from 1944-1945.
CJ-2A: Civilian Jeep built from 1945-1949
CJ-3A: Civilian Jeep built from 1948-1953, slight differences in body measurement.
M-38: A military version of the CJ-3A but without tailgate and other modifications. Willys called it the MC model. Built from 1950-1955.
CJ-3B: Very similar to CJ-3A but had a higher hood and allowed the use of the F-head engine. 1953-1964.
M-606: Military version of the CJ-3B built from 1954-1968.
CJ-4: Prototype in 1950 never saw production.
CJ-V35U: Modified CJ-3A built in 1950 for the Navy.
VJ: Early 2 wheel drive Jeepsters built in 1949-1950.
M38A1: Military Jeep. Also known as the MD was a forerunner to the CJ-5. Built between 1954-1957 and maybe as far as 1971.
FC-150: This was a pickup, cab forward, 80 inch wheelbase built from 1956-1964.
FC-170: This was a pickup, cab forward, 103 inch wheelbase built from 1957-1964.
CJ-5: Civilian Jeep, 81 inch wheelbase built from 1954-1971 and the 83.5 inch wheelbase from 1972-1986.
CJ-6: Civilian Jeep with a 20 " longer wheelbase than the CJ5 built from 1956-1975.
CJ-7: Updated CJ-5 with a 93.5" wheelbase built from 1976-1986.
CJ-8: Pickup design with a 103.5" wheelbase called the Scrambler. Built from 1982-1986.
CJ-10: Pickup version 110" wheelbase built for the military and sold overseas there was a shorter model call the CJ-10A.
C-101: Jeepster built from 1966-1973.
M-151: Military vehicle built by Jeep and designed by Ford. Full independent suspension with a unibody design.
M-422/M-422A1: Built by AMC for the Marines in 1964.
M-715: 1 1/4 ton truck built by Jeep in 1967-1969.
DJ: various models of 2 wheel drive Jeeps similar to some CJ models.
MJ: The Jeep Comanche pickup. Built from 1986-1992. J stands for Jeep and M is just a model number.
XJ: The Jeep Cherokee built from 1984-2001.
SJ or FSJ: A Fullsize Jeep Wagoneer or Cherokee built from 1963-1991.
J: A fullsize Jeep Gladiator pickup built from 1963-1987.
YJ: The Jeep Wrangler model built from 1987-1996.
TJ: The Jeep Wrangler model built form 1997-Current.
ZJ: The Grand Cherokee built from 1993-1998.
WJ: The Grand Cherokee model built from 1999-2004.
WK: The Grand Cherokee model built from 2005 -current.
KJ: The new Jeep Liberty.
Here's another site with some additional info: