looked into this as i have a ja22w jimny from japan here in the UK with the 660c. the sj80 suspension is straight bolt on. the mounts are all the same location on the axles and the body. google partsouq as it has all parts diagrams when you chuck in your vin to look at axles etc, and then find the diagrams for the sj80.
i searched for ages for suspension parts and other than japan, australia was the next best place for it. also found some in croatia that could sort me out.
the front strut on the sj80 is completely different to gen 3 jimnys (look up kyb shocks), but the rear setup is a simple shock and coil which you could figure out how to change from any specialist quite easily i'd say. the picture is a front shock, where the spring sits on the bottom plate and then sits inside the cup on the body. only thing i was unsure of was the weight of the engine in an sj80 and spring rates.
with a bit of digging from cross matching part numbers etc. i am sure that i found that the trailing arms were the same from sj80 to gen3 by part number too, so anybody selling upgraded ones should be good.
i put a hold fire on lifting/updating like for like at this stage as mine has an upgraded set already from Japan and rides just fine.
shoot me a pm if you have any questions.