Is it beneficial to index the spark plugs?
On a small block Chevy race motor, yes. Keeps the piston from whacking the ground strap and losing a cylinder.
It's not necessary on a center plug hemi-like head that the FJ (and just about every other motorcycle) has.
DavidR.
On a four-valve head, you'll get gains from indexed plugs, but they'll be so small as to be really, really difficult to measure. Don't bother, unless you have a specific need for it.