Removing the Redfield sight shouldn't be difficult, but you may run into an issue with the USGI rear sight.
The 1903A3 receiver should have a male dovetail on the rear receiver bridge, near the bolt handle. If that dovetail has been milled/ground off there is no way to install the USGI rear sight. If it is missing, about the only recourse would be to have a dovetail welded/fitted onto the receiver.
If the dovetail is still present, rear sight installation is not difficult. Once installed, the 1903A3 rear sight was usually held in place by a staked set screw.
Another thing to think about is that removing the peep sight will likely leave a couple of holes where the sight mounted to the receiver. Not a show-stopper, but some might consider it an eye-sore.
