I concur. This appears to be an Asian frame and late 1980s based on the presence of a pump peg, two bottle bosses and two tone, pastel paint. I also agree that the marks inside the steerer tube are probably due to a stem wedge, as they are part way up the tube and and only on one side of the tube.

Regarding the serial number if it is L6, it may be a Bridgestone manufactured frame, while LS may represent the Japanese manufacturer used by Bianchi.

Edit: Given the apparent era, the lack of brand embossing suggests a contract manufactured frame for a smaller marketing or private label brand.