Are you sure that you will need to do this, John? Have you used the Pension Service Advice Line to get a pension forecast for your State Pension? Yes, you are right that from age 60, Ni contributions are credited to you.
Here is my understanding of the situation. A male currently needs 44 qualifying years of NI contribiutions to get a full Basic State Pension. You therefore need to work out, or get the Pension Service to do it for you, how many years you have. You can then work out how many of the years you need to contribute to to reach 44.
However there is another complication. In May 2006 the Government produced a White paper that proposed reducing the number of qualifying years down to 30 for anyone who retires normally after 6th April 2010. This must impact you. If this goes through, you would surely not need the 5 qualifying years you are referring to?