Flown hours are allways flown hours...
Be it under JAA or FAA, hours are still hours and as long as they are in your loggbook nobody can take them away (granted that you have logged them according to the current regulations and that they can be crosschecked by looking in the aircraft loggbook or a flying school register...).
I did 45 hours of ME flying in the US and I've simply used them straight out of the loogbook, no validation required. Many schools in the US have in their procedures to endorse the hours, it can never hurt, but it's not really required.
You can also have someone certify at the bottom of each page that everything is "true and correct", that may make things look a bit better perhaps.
regards/LnS