I just finally received the frame and I'm an happy man.
Turns out it's my grail bike... oversize + Lugs... Nice paint, late 90es.

Thanks for your input everyone ! As it turns out, the diameter suggests EL-OS (31.7mm).
Far from the seller's best guess (SL !).
Here are some more pics.
I really love the contrast between the SL-looking fork and the OS tubes