Hey guys i just want to know the diffrence between a 3.8L V6 and the 3.9L in the 99-04. I have a 2000 mustang that I crashed and ruined the front end but it didn't touch the motor and it looks like it will work perfect. I am going to buy a 2004 mustang with a 3.9 but the engine needs a rebuild. SO I was thinking I can temporarily swap my old 3.8L into the 2004 mustang while I rebuild the 3.9L. What kind of work would be needed to make the swap possible? Will the ECU for a 3.9 run a 3.8? and what other work will be involved. Thanks for your time.