Croqueteer, in which case you will remember the Dutch Atlantic that ditched and how the 4-engine lobby said it justified 4 engines rather than 2.
The Atlantic was a purpose designed airframe which, as you say, will have another 20 years life. The P3 at least has proven a successful long-life airframe where as turning an outdated 50s passenger jet into an MPA and then reusing the same bits through 3 generations of the same aircraft had to be questionable.
Taking a P3 and refitting it may be one thing, doing a cut and shut on Nimrod something else again.