that is normal. When ignition is on, the fuel pump starts running 4-5 seconds and will then switch off when engine is not started. This is to get enough fuel pressure into the system from tank to fuel pressure regulator.had suspected the fuel pump as it was too silent, no noise at all. Usually you could hear it whizzing, and from time to time it used to make louder noises. Checked the voltage, it would come for 3 or 5 seconds just after switching on the ignition, then only while cranking.
Opel pump could work if it fits somehow, have already seen a Hyundai pump in an E32 730 V8 in South Korea and in Australia they use GOSS pumps for Holden cars.
Maybe some small adjustment are necessary, but in General it will work if it fits into the bracket. If too small, usually the oump kit sellers for multi purpose after market application add rubber, connectors, wire.