yes to the above.
Also you need to have stringers in the right places to mount the 4.3.
Then you need new gearing in the drive.
The wiring harness might be the same. If the new motor is close in year to the old one.
Just leave every wire in place and remove from the motor what you have to remove.
What i think might happen is you will have to lenghthen some wire.
The flywheel and coupler, might be ok ?
What i am trying to remember if the 120 coupler will fit the 4.3?
What coupler you have on it now ? A one piece triangle, or rubber one ?
Maybe someone else will chime in.