What years of jeep grand Cherokee have interchangeable parts?

93-95 are interchangable (they are OBD-I)

96-98 OBD-II starts

99-01

02-04

05-current (AFAIK)

Some parts are interchangeable between 96-01 since most is practically switched over other than the body style and suspension components and emissions controls.

Drivetrain components other than transmissions (with some work they can) between the 93-98 years. Same goes for the 99-04 years.