Will a 98 3.8 v6 mustang motor fit in 96 mustang?

Yes, a 1998 3.8L V6 Mustang engine will generally fit into a 1996 Mustang. Both cars used the same generation of the 3.8L V6, and the engine bay dimensions are largely the same. However, there might be some minor differences in wiring harnesses, sensors, and possibly mounting brackets that could require some adaptation or swapping of parts. You might need to use some components from the 1996 car to make everything work correctly.