I have to replace the engine in a 2004 Explorer XLT 4x4, 4-door. The current engine is the V6 4.0 cast iron block. My two questions are will an aluminum block motor fit? Is there a difference between the engines in a 4x4 as opposed to the 4x2?.. Or are all 2004 v6 4.0 engines the same, cast iron or aluminum, 4x4 or 4x2, all the same? Thanks!