Personally, if I was looking for that much lift I wouldn't be looking to get it from shackles. There are mixed reviews on it but in many cases it affects caster angle on the front axle and leads to handling problems. Not to mention they'll be sticking further out to hit obstacles. Remember that for every half inch of lift a shackle has to be an inch longer than stock. So 1.5" lift shackles will be 6" long bolt-bolt.
'84 CJ-17: 17" stretch, locked Toy axles, 5.5" lift, FI, AX15, D300 w/twin sticks, boatsides & junk.