The Enterprise was not an retrofit. It was intended to be a nuke from day 1.
During its construction it was deemed too expensive to build the other five of its class so they shelved the design and built the Kennedy as a conventionally powered ship. The Kennedy was ordered as a nuke but was changed to an oiler after the keel was laid. Meanwhile they went back to the drawing board and designed the Nimitz class.
i thought keel was laid in the 40's but I was 20 years to early. so why was it "overpowered"? accident or by design? thanks.