The Prez's new ride shall be new built....as a requirement of the contract. Even if the 53D was a candidate. Sikorsky would have to re-open the production line for the aircraft in order to meet the contract specs.
Remember how strict the maintenance policies are for the aircraft when used for the President....starts with limiting timed components to Half of their normal Life Values....surveillance of the construction process of critical components, and a total segregation of parts to be used on the aircraft.