MS Project 2013 - Manually set up the finish date ???

[nicolafusconi]

Hi everyone, I apologize for the stupid question considering that autonomously time ago (at that time I was using MS Project 2010) I had solved the problem. But NOW with MS Project 2013 I cannot find the solution I urgently need.

Scenario:
Start date - April 1
Finish date - April 30
Duration - 60 days

I need to use 60 days as the duration, but I want to set manually the start and finish dates AND avoid automatic calculations by MS Project. MSP 2013 of course because I set up "duration=60 days" then overwrites the finish date April 30 and automatically calculates it as May 30 .
My requirement is: due to the fact that the task is assigned to 2 resources (100% booked for the task) then the agreed duration with the client (60 days) is expected to halve (30 days >>> 1st april>30th april).
Don't know if I'm making a wrong use of MS Project and someone could guide me on how to proceed if there were an approach more brilliant than mine...... BUT If my approach is correct, how can I avoid Project automatically calculating the Finish DATE?

Thanks so much