There is no crossing over from an EASA part 66 to an FAA A&P or vice versa.
The hardest task on the FAA A&P license is to get the slips = Approval to take the exam .
You only get those when you are working on N-registered A/C and you can prove the need for the licence.
The exam questions are published yearly and you learn them by heart!
There is also an oral and practical exam.
More info is on
HowToGetAnA&P
Cheers