Assuming that '88 is a later '88 with the 10 bolt front axle and 12 bolt rear, then the height is measured from the ground to the center of the headlights. It needs to be 33-34 inches, per the FSM for a '90. (It would also be a square headlight Trooper.)

If yours is an early '88, which is like the earlier ones with the 8 bolt front and the 10 bolt rear, then someone else is going to have to chime in.

Jim Paget
88 YJ with a few changes

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