Rao,
On FJ40s, a spring flip is usually to mount the springs with rear ends facing forward i.e. rear spring stays in the rear but its mounted facing the wrong way.
As stock FJ40 springs are off-centered / assymmetrical (more spring length to one end of the centre pin and shorter on the other) the flip at both ends results in an increased wheelbase.
One has to obviously adjust the springs and shackles a bit to get the ride height and keep other stuff correct. Some other changes and gimmicks are also required.
Alternatively, you could use longer 60 series or 55 series springs to achieve the same effect. This seems to be quite a routine modification on FJ40s abroad (though has never been tried out here from what I understand) to gain wheelbase (for offroading) and fit larger tires (some random pics of suspected flippees below).
96 inch stock spring flip on 38s
100inch wheelbase with 60s springs:
102 inch with flipped 4 inch 40s lift springs:
105 inch extreme Nordic Cruiser:
