Byron I don't know where your getting your reference dates for CV-67, but per navsource.org (and several others) these are the dates for the JFK:
Awarded Laid down Launched Commissioned Decommissioned Stricken
30 Apr 1964 22 Oct 1964 27 May 1967 7 Sept 1968 23 Mar 2007 16 Oct 2009
Several sites list as Ordered instead of Awarded, but all agree that the date is 30 Apr 1964
Friedman. Which is
the source on carrier design. I think that my choice of words was poor on this one. The quote is: "Secretary McNamara rejected the navy position, and construction of CVA 67 (the USS John F. Kennedy) as a "fossil-fuel" carrier was ordered on 9 October 1963, about a year behind the FY63 schedule." (p. 283)
That said, if you can find a reliable source (and I've looked for sources on that section about her being ordered as a nuke, and haven't found any), we'll look at this again.
Per Neptune Papers #7-Aircraft Carriers - The Limits of Nuclear Power - ref #29
29. In September 1964, the Center for Naval Analyses completed a major study on nuclear propulsion for
surface ships with primary emphasis upon carriers. The report, nicknamed NAVWAF 33 for being the 33rd
study by the naval warfare analysis group, found that a two-reactor carrier comparable in size to the USS
Enterprise would cost about the same as a conventional Kennedy class carrier, plus a fast ammunition-oiler,
plus a replenishment fleet oiler; Rickover and the Nuclear Navy, op.cit., p. 145.
This was the justification for changing CV-67 from nuclear to conventional power and it predated the assassination. Something else to note is that CV-67 was originally planned to have 4 reactors to Enterprises 2.
No, by any dates you want, Kennedy was well under way by then. If they were going to build her as a nuke, the reactor design would have been finished, and fabrication well under way. There would be no savings from switching.
There was an alternative nuclear design underway, SCB 211. It was a clean-slate design, not based on the Kitty Hawk. It was not built.
Edit:
Why would they even build a nuclear carrier on the hull of a Kitty Hawk? They did a new hull for Enterprise, so either they'd repeat that, or start over. In no case does the "begun as a nuclear Kitty Hawk" make sense.
Edit 2:
The above quote actually supports my point. They used Kennedy as a baseline for the conventional carrier. Therefore, it was already planned to burn dinosaurs when the study started. The study probably took something like 6 months, so it was before that. And given the problems inherent in converting a CVN to a CV, a reversion to an older, purpose-built design would have been a likely baseline if Kennedy wasn't conventional from the start.