Didn't '73 see the intro of the isolated K-frame and slightly different inner fenders? So they may have not been designed with the Hemi in mind as '71 was the last MY Hemi. If it fits in a '73, it must fit. But it sure looks from the picture like the valve covers hang over the frame rails. Might make going in from the bottom a bit of a chore.
I had a '74 (small block) and it did have the isolated K-frame which appeared to me to be simply large rubber bushings at the point of attachment to the sub-frame. I do not recall the inner fenders being different than on '71s, but, details do tend to fade over a 27 yr. span. As you stated if it fits a '73, it must fit [a '74]. I could never distinguish any appreciable difference in a '73 and '74.