The rear axle stay plates are very different from later bikes. They have no provision for a tow bar and they are made out of 3/16″ steel plate. The rear rack stay tubes are drilled for safety wire to secure the axle bolts that are also drilled for safety wire although no wire was on the bike when I got it.
The adjuster bolts are 7/16-20 UNF instead of 7/16-11 UNC on MK1s and 3/8-24 UNF on later bikes. They are Grade 9 Supertanium Alloy which is massive overkill for what they do. My guess is they either came from Charlie Fehn’s aircraft repair business or the Nethercutt’s race car adventures.