What are you talking about?
First of all, the 2005 Mustang is going to have a 4.0 litre V6 not a 3.0. (Maybe it was a typo...) Secondly, why would Ford use an engine from Cadillac? And Lastly, the V6 used by Cadillac is a 3.6 litre and NOT a Northstar! Only the 4.6 litre V8 is a Northstar. Whoever told you that must've been half asleep because I've never heard any of that!