Ed the 9/16ths are not original MKS spindles, they were from a set of Victor DX's off an old MTB Hootski got hold of so will work in the Shimmys. They don't have the distinctive ends where the spanner sits so Dave wo't want them I imagine.
Strip the one out and send them with the end cone and nut (don't mix them up!) to Tom to check and he can send back the set you need after he's 100% sure, or measure the one that is not in the pedal right now as it's the same.
Give me a call later tonight if you don't get what I mean, but the pedals were originally not a pair so I left one of the original 9/16" axles in one. You do have a pair of matching 9/16" to send Tom out of the Victors though wjen you strip the axles all out.