1) My stock rears measured 1015 eye/eye, stock fronts 940 eye/eye, so 75mm longer. Both were somewhat shagged vs new original springs though so yours may vary.
2) 2" extended shackle is stock 70mm plus an extra 50mm (2") for a total length of 120mm (between bolt centres). You'll likely need 2" shackles if all you've done is redrill the rear mount point in the original hanger. I made up new hanger plates so could move the rear of the spring back a bit - that lets me run a 100mm shackle with good shackle angle. I've got some 2" shackles here that you can have for $50 if you want (need bolts though) ... but I'd honestly recommend you splash for some of Fatzook's TwinStick Offroad ones
3) 40mm OME springs deliver approx 40mm lift. They are about the same eye to eye. Mine were slightly shorter eye to eye than stock actually when not fitted - that could have been due to the original springs shagging out though and losing some of their elastic recovery.
More info from my dodgy RUF job here if it helps. Bottom of Page 1 / top of Page 2.
By the way you'd only want to move your rear hanger back HALF the difference in spring length and compensate for the other half at the front using longer shackles. Otherwise all the extra length will be on the back side of the diff meaning the diff will be nowhere near the centrepoint of the springs. Could be wrong but I doubt that's going to help spring life or performance.
If fabbing mounts up though (and by fabbing I mean welding, not a dodgy bolt jobby like mine) then I'd go for extending the front mounts. That way you get a bit of wheelbase extension as well as the longer, flexier spring. Moving rear mount won't give you that extra wheelbase length. Remember if making up new plates for the rear to drop the mount point slightly too to keep caster angle the same when you put the longer shackles on
im doing a fabricating apprenticeship so will do pretty well all the metal work (shackles,spring mounts)myself