During the mid 70's my sister had a Mercier 100. It rode very nice and I fondly remembered it. In 2003, I purchased a Mercier 300 (74) and it rides similar to my Colnago dream. I have never seen a Mercier during this time period with Special tour de france decal unless it was just for the euro market. The STF decals were on bikes from the 80's.
It is hard to say if this is reynolds tubing or not. I do not see evidence of a reynold sticker where it should be on the bike. Some of the decals look as if the bike is from the mid 70's. Most of the parts do not look original but the drop outs look decent. I have a feeling it is a 200 model. (The bike came 100, 200, 300). Also look carefully at the front hubs. I see some rust there. If I were you, I would be asking the seller some questions but It probably rides very nice no matter what the model is.
Linda
Millis, Ma USA