As for the relief for the magazine cut off, once the steel patterns were made for the stock machines, they went ahead and used them, probably until they were too worn, or until the "press of work" was reduced to the point where the time could be afforded to make new ones without the relief cut.
The original specs for the No.4 given to Savage and Long Branch were no doubt copies of the drawings (and actual rifles) from the No4 trials rifles produced at RSAF Enfield in the 1930s. This is what they first produced, complete with hinged bands, waisted foresight protectors, "button" cocking pieces, forends like yours etc. Later, simplifications and economies were introduced.
Personally I've never understood why Long Branch and Savage were encouraged to introduce the MkI* modification when it was not introduced where economies were really needed: in the UKordnance factories! The same with the stamped trigger guard etc.
Anyone got an answer for that?