It seems that the general requirements for the new bomber by the STA didn't say what types of the MGs there should be used. So the prototype was designed to carry the armament chosen by the plane designer in order to match the specification. While the STA said the HS 404 should be installled , the prototype was changed to host the kind of the cannon.
To answer your question docavia book ... it looks like that's the study only for the LeO 450 if you meant the data on the page 71. If you scroll back to the page 68 you may find the data for the LeO 451 powered by the G-R 14N engines