Maurizio:
I do own a copy of the John Allen "Porsche 956/962" pub 1988 (one of my favorite Porsche race car books; but unrelated to "Porsche 956/962 - The enduring champions" by Peter Morgan pub 2003) and would be happy to check this information for you.
IIRC, Joest won LeMans 1985 in similar to 1984 "NewMan" (jeans) livery, and I believe again used Dunlop Tyres.
(1984 Livery)
(1985 Livery)
I also have scans of the Studio 27 1/24 decal placement sheets for the 1984 and 1985 LeMans winners which quite clearly show the Dunlop markings on tyre/body.
Now in 1986, Joest did use GoodYear tyres and the upcoming "Spirit of America" offering from Slot.It should be thus equipped.
One must be careful when referencing cars in museums or at historic racing events because they frequently are not original specification or livery.
BTW, the 962C (in long tail form) won the 1986 LeMans in Rothmans Livery.
Thank you for your fine products and much success in the future.