A stock YJ is called spring under axle. (SUA). lift blocks are only designed to work with SOA (spring over axle) suspensions. And you should NEVER put any kind of lift block on a front axle.
So, even though you can get it cheap, it wont work for you.
'87 YJ, 4.2L built and bored, 8" of lift, 8.8 rear, AX15/NP 231J, Tom Woods drive shafts, Flat fenders, 12,000LB winch, Custom bumpers, Rattle can paint job. Never completed...