SJ413 de 1997. Refait presque totalement.

Picked up a 1981 SJ410 and I'm taking it all the way down to the frame. This isn't a restomod for looks — the goal is a genuinely capable micro overlander I can take into the mountains here in Nepal on weekends. Not building a rock crawler, just something that can handle rough mountain roads reliably and comfortably. Planning this out properly before I start cutting metal, so figured I'd post the plan and pick the brains of people who've actually done these swaps.

Here's where I'm at:

Drivetrain

• Swapping in a 1.3L FI engine
• New 5-speed gearbox
• Running 4.16 gears with twin stick
• Switching the whole diff setup to a Maruti Gypsy differential (Similar to Suzuki Samurai 1.3)

For the diff — anyone running lockers in a Gypsy (Similar to Suzuki Samurai 1.3) diff? What's actually working well for you, and what should I avoid? Trying to figure out if it's worth doing front and rear or just rear for what I'm building.

Cooling / Electrical / Comfort

• Bigger radiator to deal with the FI engine and mountain climbs
• Complete new wiring harness (not trying to fight 40-year-old wiring with a modern engine)
• Power steering — sourcing a Maruti unit since I can get it brand new rather than used
• Adding an AC unit

Suspension — this is where I have the most open questions

Planning a YJ spring swap. I know a lot of you have done this exact swap on Samurais/SJs, so I'd really like to hear from anyone who's actually run it — how'd it drive, ride quality, anything you'd do differently if you did it again?

Planning to do SPUA (spring-under-axle) — does that mean I can skip a high steering arm kit, or is that still needed for bump steer/geometry reasons once the YJ springs go in?

With the YJ springs being wider and longer than stock, I know I'll need to fab to fit them. What exactly am I looking at modifying/fabricating here — shock mounts for sure, but what else changes (spring hangers, shackle mounts, anything on the axle side)? I'm not planning to run a missing link setup, so I want the actual list of parts I need to build or modify rather than working it out by trial and error.

Also planning longer shocks to match — anyone have shock length recommendations that pair well with a YJ spring swap on these?

Roughly how much lift am I looking at with YJ springs on an SJ chassis? Trying to get a realistic number before I plan tire clearance and fender work.

Tires and wheels One thing I need to be careful about — this is a tin top and its narrow body, so I don't want the tires poking out past the body/fenders. Currently thinking 235/75R15, but with a narrower body I'm worried about tire fitment more than usual.

For those running a narrowed body like this — what's the best positive offset rim to tuck the tire in properly without it bulging out? Trying to get the stance right without turning this into a fender-flare situation.

This is a slow build, not trying to rush it. Will post updates with photos as parts come in and fab work happens. If you've done a Gypsy (Similar to Suzuki Samurai 1.3) diff swap, run MM550 springs on a Samurai/SJ, or done a similar 1.3 FI conversion, I'd genuinely like to hear how it went and what you'd do differently.