I've done this swap MANY times as I've changed out my IRS MANY times.
18mm, and 21mm are your friends for this.
Also will need a 12mm to drop the rear caliper (assuming that you have rear disc). One thing to remember here if you DO have rear disc, is do NOT press on the brake pedal during this procedure, otherwise you need to re-adjust the caliper when you go to re-install it.
1997 LX Sport 4.6L 2.73 , MODS=SCT tuned/J-Mod/Trans Cooler/Dyno max Cat-Back/NgkPlugs/Mac cold air/March UD's/FRPP aluminumcarrier3.73's(spare for strip use)/ PI cams + PI intake manifold w/adapter plate/ Mark VIII Convertor/80mm L-Maf/70mm TB/ Mark VIII 1 piece shaft/Cobra R' wheels/ Kumhos 235/60/16 - White leather w/ blue cloth seats - white face gauges in 95 cluster