I’m not sure, that there was any specificity to what was equipped on Harley vs Indian per say, but I have noticed some subtle differences in those long reach stems.
The biggest and most obvious is the opening where the crossbar passes through.
The stems intended for use with the Shelby Motobike bar, had a wider opening to accommodate the thickness of the cross bar on that particular type of handlebar.
The type used with the typical Pope style Torrington bar, had a narrower opening.
The profile where the reach portion of the stem meets the quill changed some over the years, and I’m not quite sure of the reason, other than style.
The Harley is shown in the catalogs, with the type that you have there.
The Excelsior Motorbike’s of the era had a tall Trussrod cap nut, so they may have moved the reach portion of the stem flush to the top of the quill section, to accommodate the extra height of that type of cap nut, because on those bikes, it was difficult to insert the stem all the way down to sit flush with the headset cap nut.
Just a thought.