Roger Rule in his Winchester Model 70 book lists the M 54 as the Predecessor, and features the NRA Short Rifle as a M 54 sub-variant.
Beginning about 1934, the receiver port as featured on the Model 70 was
also included on the later M 54s as on this 270 rifle.
The 270 WCF chambering is a bit faster than the average cartridge velocity for the 7mm Mauser
in the 20 inch barrel length. Very handy in mountain hunting for deer and sheep.