the mustang is a fox body and from the looks it was a 2.3 ltr engine. i want to maybe see if i can get a V6 4.0 ltr engine from a newer car in it. can this be done other than having to replace many parts to be able to handle a bigger heavier engine.
YES - but if your gonna replace with a 4.0 V/6, try to find the S.O.H.C. version. Will feel more like a V/8 than standard 4.0. Will not have any problems with installation, with just usual suspension, cooling and wiring upgrades.