They are fully interchangeable, the only differences being in the outer shell (Victor's has two art deco ridges while HMV's is smooth), and the HMV version has a narrower aperture inside the backplate, because the swan neck tonearms HMV designed for that soundbox have an inner part and an outer part - the outer part is the same diameter as the previous gooseneck, and thus the same size as any Victor up until the Orthophonic, but the inner diameter is much smaller, apparently tapering slowly through the length of the inside of the tone arm.
Victor apparently did not design a tonearm/horn system to go with its No 4, the way HMV did with theirs. Fascinating difference in approach.