At a guess, there won't be any difference in spring length from RWD to 4WD - there might be different spring hangers/shackles and maybe the number of springs. I would also, at a guess, say that Gen 2 springs would interchange with Gen 1's. If you can get a look at a Gen 2 in a JY and take a tape measure to them and the hanging hardware, it might solve your dead spring issue (do not forget to check the U shackle bolts, bump stops and axle plates as there might be a difference there as well - you'd need to factor in the extra hardware for a spring swap)