But try it before you start to sand. I found an old Nitto that slid right into the steerer on my Gitane.
Nice vintage stem , too. Looks like a Cinelli 1A. Can't remember the model name. Cost me five bucks.

And though I would also recommend French bar and stem on a bike like this, in the mid 70s there was at least one model Moto that came with Nitto bars and stem as stock. The Grand Record.