Bumper Swap

Exactly how much time does it take and how hard is it to swap a 70-72 rear bumper onto a 73-76 Duster? I have put my project on the back burner for long enough and either it is getting to me so much that I am blistering and peeling or I have a sunburn..

I have never attempted to do such a thing and I have a 71 that is rotting in peace.
Thank you for the input, Jared.