I've done it a few times on FSJ's.
Are you sure you're ready for a springover?
The $$$ and time add up quickly if you want to do it properly.
A poorly done SOA is a quick way to ruin a perfectly good truck.
Labor to relocate the front axle under the spring is in the neighborhood of $250.
You need to do a rear shackle reversal at the same time or you will have to use big scary blocks. Labor for a rear reversal is about the same as the front.
After that is done, you will need to deal with the following issues:
- Steering: I have seen some people get by with a 4" drop arm, sometimes the draglink will bind on the spring, sometimes it won't. You will still have bump steer. To eliminate that, you will need do a crossover steer or go full high steer. I have the parts on hand to do full high steer. I will not do it any other way.
- Brake lines: you'll need extended lines or re-route your existing lines
- Driveshafts: Chances are they will be too short so you will need longer driveshafts. The front CV is pretty much guaranteed to bind unless you spend a bunch of time clearancing the yokes or change to a high angle CV.
- Shocks: You will need some.
Instead of all that, you could just put a 4" lift kit on it. Rusty's has a 4" all spring kit for ~$500 and a front spring/rear block for ~$350, shocks included. This is pretty much a bolt-on, you don't get into all the aforementioned issues, will allow you to comfortably run a 33" tire on a wide track with no fender trimming, and makes for an extremely capable rig.
Feel free to call if I can help in any way.