GNSC ugrade for Audio Research preamp

Has anyone had experience with the GNSC upgrade to Audio Research preamps. I was looking to buy a REF-3 but have seen a REF-2 MKII upgraded by this company and wondered how it would compare.
Had a fairly close direct comparison between my LS-25 Mk I with ref. level mod and a stock Ref-2 MkII a few years back. I think the powercord were slightly different. Some $$$ on the Ref 2 vs. my DIY $30 belden cord on the LS-25.

The sound was very, very close. The Ref-2 MkII was slightly more forward, faster, and more air. But everyone thought that the differences are cosistent with the 6H30 supertubes inside the Ref 2. The modded LS-25 came with a quad of Siemens 6922 GNSC recommended. Sounded more lush and sweet. But I think the sound would have opened up more if I had put in some Amperex tubes.

If the work is done by another company I would call it a mod not an upgrade.

Upgrades are performed by the manufacturer.

If you want to buy an upgrade for ARC I recommend talking to ARC. Maybe they have an update and your resale value will remain high.

Modified equipment can be hard to sell. I know I would never consider buying a modified anything.