You are right try karney mein koi harj nahin. Stock shackles dont cost too much and are rather quick to replace. Nevertheless, I am not a fan of shackle lifts / body lifts and I am not sure what real benefits ground clearance brings in our sort of offroading. You say now that you will not speed around town, but once all the work is done and you finally get the car on the road ..... Its just quite impossible to resist gunning the V8 driving down a straight empty road and these shackles (even with aftermarket polyurethane bushes) will make it difficult to keep the car going in a straight line mainly because the caster angle is thown out of the window as you lift the FJ. Caster correction shims will help but only upto a certain height, these shackles seem way too high at the moment.... Anyways all the best for the future and its best to learn by trying it once as long as you are aware of whats going on!
BTW the rear shackles you can possibly get away with but its the front that is the problem owing to steering caster and body sway!