firstly ask this, why do you want coils as apposed to leafs?
ive got leafs in my car and they have been reset with an extra main leaf added, combined with pedders gas shocks that rear end is now so stable and the car handles great.
there is really no point in converting to coils apart from gimik and you can achieve the same results. use a ta22 diff, chop the moints off your ke55 diff and remove all the linkages ect and mounts off the ta22 diff, weld your mounts to the ta22 diff and away she goes. maybe invest in some anti tramp bars but i havent had a problem with mine as of yet.