I voted no on a pre-packaged kit. The tough part about building a pre-packaged kit is there can't be too many variables for the kit to work well. Center of gravity, drivetrain length, gas tank placement, and steering box used all vary greatly between FJ40s. Unlike mini trucks where most all trucks run dual cases, IFS boxes, have roughly the same lift, and utilize the factory gas tank.
40s are built in about any variation you can come up with. Theres motors from just about every car manufacturer in small block, big block, and even v-6 configurations. Transmissions vary from relatively light Toyota aluminum trans up to pretty heavy NV4500s and all kinds of autos. T-cases vary as much as well.
For steering boxes theres the standard GM car Saginaw box that end up towards the front of the frame horns. Then theres the FJ60, FJ80, Astro van, and Scout II forward swinging boxes that end up directly above the axle housing on the frame rail. A lot of 40s have the standard in cab gas tank but later model 40s had the tank under the tub right behind the t-case. And then theres the center of gravity which is all over the place on these things.
At any rate, if you can make a kit and make it work, more power to ya. My feeling on a vehicle that has so many variants any time they stray at all from stock form is that a link set-up has to be custom built for the specific vehicle.