DeSantis Shoulder Holster harness compatible with Galco holsters?

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I have a DeSantis shoulder rig. I need a holster for a different gun that is available from Galco.

Do I have to buy the entire shoulder rig from Galco or can I just buy the "shoulder holster" component from Galco and use my existing DeSantis harness?

Does anyone know if the harnesses from the 2 companies are interchangeable?

Thanks!