In the photo above you can see the same stem that I have, a Cinelli 1A stem with the wide milling on the sides, and narrow milling on top. You can see the side milling is filled in with Molteni orange paint and the top milling is filled with black paint.
I believe this is a promotional mini-poster dating from the early to mid 80's, put out by the Merckx factory in its early years of production.
(By the way, the mini-poster is dedicated "To Ray, best wishes!" and signed by Eddy, but it originally belonged to a different Ray than me! A friend called Ray gave it to me after his girlfriend trashed his apartment, including his bikes, and this mini-poster was one of the few things that survived intact. Sad but true.)
In the photo above you have a better view of the narrow milling on top of the stem, painted black. (Note the first generation Super Record rear derailleur.)
This is another mini-poster from the 80's.
And in this photo you can see a variation on the stem, with the side milling painted orange, but with no milling on top. (And check out the beefy seat stay with the flat cap - I'd say that frame was probably made by Ugo De Rosa.)
This photo is from page 86 of the January 2005 issue of Cycle Sport America. The photo was obviously taken during a Tour de France, but the date is not given.
UPDATE: My thanks to Ray Green who wrote (all the way from England! :)), to inform me that the year of this photo is 1974.
UPDATE: Notice that Patrick Sercu used plastic tape to finish the cotton tape on his handlebars, while Eddy's has no such tape. According to Ken Denny, that is because Eddy wrapped his bars from the center. That makes sense - I don't think he used glue like I did. What I'm not sure of is how he finished his wrapping at the bar ends. I don't see any plastic tape, so it looks like he stuffed the end of the cotton tape into the bar ends. If so, I'm going to guess that he had hard plastic bar plugs, not the soft rubber ones like I have.