Q
The stabilizer fuelling lockout system was installed to maintain the accuracy of the FQIS system, but additional testing found that that the stab. FQIS was accurate regardless of stab position.
Depending on which group a particular aircraft fell into dictated the work required, basically removal of the stab. position switch, capping and stowing (or removing the wiring looms)plus some changes to the p54 and p42 panels. Some airlines also had a flight deck refuel (M5???) panel that required modification.
I don't think there were any plumbing changes!