A Line Mechanic reports about a flight crew noticing their cabin entry Doors L-1 and R-1 placards read 'Slide' and not 'Slide/Raft'; even though Maintenance Records indicated the B757 had 'Slide/Rafts installed.

Narrative

Aircraft was scheduled for an ETOPS flight. [During] preflight; flight crew noticed the [cabin entry] Doors L1 and R1 door placards read 'Slide' and not 'Slide/Raft'. Previous research by other parties had noted that Slide/Rafts were installed on this aircraft. However; after researching to see which placard was correct; I determined that there was only a slide installed not a Slide/Raft. The aircraft was delayed to get a life raft onboard and the proper paperwork and weight and balance change; and the aircraft than departed to ZZZZ. Once it arrived in ZZZZ; it was determined that two life rafts should have been installed; not just one. In hindsight; there was a disconnect between the General Maintenance Manual (GMM); Flight Operations Manual (FOM) and the Illustrated Parts Catalog (IPC). The GMM noted that only slide/raft be installed; the IPC only showed one raft can be installed; and the FOM; which I wasn't aware at the time; noted that two rafts be installed. By the time I arrived back to work the next day; the company was aware of the Manual problems; and was submitting the required Manual change paperwork. Also; I would recommend an ETOPS Checklist for overwater flights to verify the proper equipment installed.