I've been told that most, if not all, 777IGWs (777ERs) have been reconfigured. These are the ones that run between the West Coast and Europe and the West coast and Asia (SEA-NRT for example).

The older 777s (777As?) haven't been totally reconfigured. These are the ones that fly from Dulles to Europe.

If you are flying JFK-LHR in the 763s, why not trek over to EWR and take the 777...the First Suite has consistently been on that EWR-LHR flight.