Imaginative seller! It's not a Cinelli.

Sorry to be the bearer of bad news.

Most other suggestion are going in the right direction.

26.4mm was the standard size seatpost for metric diameter tubes with a 1.0mm x 0.7mm wall thickness used for most production French frames back then. Reynolds 531 or maybe Metric Columbus SP.

Fish mouthed rear stay and forks ends are definitely French.

Could be a Stella frame or a top end Motobecane from the late 60's to early70's. Or it could have been produced by some small French constructeur (local frame builder). .

The workmanship looks good in places but someone got carried away with a file on the lugs. Were they trying to thin the lugs or did a ham fisted amateur attempt a frame repair???

I'd have someone who knows what to look for as regards to damage or repairs check out the frame before I put any work into it.

Chas.