Someone (name withheld to save him from embarrassment) posted pictures of his wire wheel hubs asking why one side had nuts on studs and the other had low-profile bolts. That immediately said to me that he had a standard hub one side but a conversion hub the other, axle type unknown. Conversion hubs are machined to allow the wheel to sit as close as possible to the drum, in an attempt to reduce how much further wire-wheel tyres on a stud wheel axle stick out compared to stud wheel tyres. However only about 10mm is available, whereas the difference in the wheels is about an inch. In this picture you can see the nuts on studs on the left, and low profile bolts on the right. Also the distance between the angled wheel seat and the drum on the left is clearly more than that on the right. It's for this reason that low-profile bolts have to be used on conversions hubs, there simply isn't enough room between drum and hub for the much taller Nylocs and studs:
And this is the effect with the wheel fitted. Richard Tower shows his wire wheel with only 15 thou clearance to the drum when it was on conversion hubs on a stud-wheel axle, whereas mine on standard hubs have 11mm.
Tracking gauge pointers in the middle of the wheel mounting surfaces:
A spacing of 1320mm: