The FAA International Field Office in Singapore is for maintenance only. The FAA Flight Standars District Office that is in charge of Operations for Asia is in San Francisco, CA. Here is the address and phone number:
FAA SFO-IFO
831 Mitten Road, Room 105
Burlingame, CA 94010
Phone 650-876-2771
Fax 650-697-7231
I don't know your situation, but this spring I assisted two fellows through the process in the US as they were becoming crew on an "N" registered Learjet in Singapore. They both held ATPL issued by "other" countries. They were required to sit the FAA ATP written test and pass the ATP flight check (done in conjnction with their Lear training / type rating).
I believe that IF you hold an ATPL with type ratings from another country, the FAA will grant a "reciprocal" CPL with type ratings based solely on that.
There is a form that must be submitted to the FAA to verify your licenses and experience in either case. The FAA will check with the Aviation Authority in the country of issue of your licenses.