just make sure there's no marks from previous wrecks like weird bends/dimples underneath or on the subframes or inside the engine compartment where the fenders bolt up. (maybe this guy is a repeat offender and wrecked it before...you never know). $4000 sounds like a fair price for it (only if it's a 5.0L). If it's a 2.3L give him max $2500 i'd recommend. good luck
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'84 Mustang 5.0 LX
My car