Here's a good thread from the Frequently Asked Questions (FAQ) forum - http://forums.hybridz.org/topic/57506-240z-260z-or-280z-chassisbody-differences/
You need to be more specific than "mecanics". All of the moving parts are mechanical. Doors, wheels, engine, transmission, etc.
The complete drivetrain, from engine to differential, from the 260Z 2+2 will transplant in to the 280Z, if that's what you're asking. Not many body parts though, if it's an early 260Z, plus the fact that 2+2 body parts can be different from coupe parts.