B767 pilot reported standby altimeter and airspeed indicator were malfunctioning. Flight crew returned to departure airport.

Narrative

During the cruise phase; I recorded the RVSM checks' altimeter readings. The standby airspeed displays zero knots; and the standby altimeter denotes 8;260 feet. All other indications and aircraft systems were functioning normally. I contacted Operations and Maintenance Control via HF Radio phone patch and reported the errors indicated with the STBY instruments (A/S and Altitude.) Maintenance Control requested an air turnback to ZZZ. Operations verified the fuel onboard was adequate; at XA18z; we amended the release accordingly. I executed a call to ATC (ZZZZ) and told them the company wanted us to return to ZZZ. ATC cleared us direct to ZZZZZ...ZZZZZ1...ZZZ. No further issues occurred for the remainder of the flight. Note that I did not declare an emergency. Please let me know if there are any questions. Also; I am requesting a follow-up on what Maintenance found to be the reason for no STBY pitot-static indications.Suggestions: After the replacement of any instrument or item involving the pitot-static system; company policy requires an RII. After the mechanic performs the corrective action; another set of eyes ensures all static connections are correctly fastened. The RII (required inspection of installation) is a good practice for critical items such as the pitot-static system.