Outer Limits 4x4 Board

I am going to replace my FJ40 springs with either 60 or 75 series springs to gain some more articulation. I've done a fair bit of reading up on it on here but I've still go a few questions:

From what I understand, FJ40 fronts and backs are the same (fronts have more leaves obviously).

Up front - I think I will use 60 series rears and extended shackles. I would like to use 75 springs but they will be too long won't they???

Down the back - 75 series rears, flip the shackle hangers and extended shackles.

Is this the best option if I want to stay with leaf spring?

Any input muchly appreciated.

Oh yeah, I already know that I'll need to change all the spring mounts for the later model springs and move my top shock mounts. I'm going to use 60 series diffs and cut and turn them when I do the SOA so I will get the castor right then.