Applying US STCs approved on other EASA member state aircraft to your own aircraft

[QDMQDMQDM]

One of the advantages of EASA is that mods approved in one state are approved in all states. I want to put vortex generators on my PA18 and there is a Swiss PA18 with them on. Although Switzerland is not yet a full member of EASA, its approvals are treated like those of other states. I have checked this with Roger Hardy at EASA.

My question: precisely what information do I need to get from the chap who owns the Swiss aircraft? Do I need a photocopy of his logbook entry relating to the mod or do I just need to cite his registration in my own logbook entry?

Thanks,

QDM