the "short" National is way more common. The long ones were only used in Eldredge machine prior to the merge with June - so before National came into existence.
From what I've found contacting sellers, I think many early Eldredge got converted to the short shuttle. Even on the Boye case, for these two, it says "If too long use . . ." and "If too short use . . ." They are indentical except for length.
I did find an Idalia machine - it looked identical to the one I just got, that the seller sent a picture that it did in fact take the longer shuttle. Unfortunately he had it in a table, pick up only on the east coast.
However, I was going over some of the "Junk" I am sending your way (remember - you asked!) and found a few longer shuttle carriers that may be what I'm after. I suppose it could be considered cheating if I converted one to take the longer shuttle LOL!!
I think I've got enough(junk) to fill a large size priority box - IIRC, you also wanted needle paraphernalia - I also have a pack of Boye Phonograph needles. One never knows what will show up with sewing supplies! My shed is suppose to be ready for painting Easter weekend - and just got the budget cycle wrapped up at work, so it's time to get some of my collection organized.