PLEASE HELP

No, the T45 will not bolt up to a 5.0. Your T45 transmission has a modular bell housing pattern which is different then a 5.0's SBF bell housing pattern. There used to be a company that made an adapter plate (Keisler Engineering IIRC) but they are no longer around. It's not worth the effort or money to try and adapter a T45 to a 5.0. You would be better off changing the trans to a T5 if you were to consider swapping in a 5.0.

Your options of engines are limited to engines with a modular pattern (4.6, 5.0 coyote, 5.4, 6.2, 6.8). Why you looking at changing the engine anyways?