After spending about 4 hours researching and finally calling a friend in Toyota marketing Im of the conclusion that FJ is just a designation that was selected for the product line, it appears to have no real meaning behind it.
But while doing the research I learned lots of information about the history of the FJ and where its ancestry lies. Some real interesting history there.
I've been reading. Some people call it Fake Jeep (hah) ... Some think that the first letter "F" stands for the type of fuel "gasoline" ... and the J stands for Jeep.
Checkout wiki for land cruiser, from looking at other sites and info I was given by a friend that works for Toyota it appears to be pretty reliable info and very interesting.