Originally Posted by CyclesMakaron

H D5456
Frame built in December 1992/January 1993.
No tube markings (should be X or XB for Corsa Extra), no frame size markings - this could mean a frame built with a "mix" of tubes in an unusual geometry.
...and this could mean that it could indeed be a frame built for Team Willy Naessens for the 1993 season.
The sticker on the steering tube and the inside of the tubes visible through the bottom bracket are worth a look.