Thank you for the pointer. I have two of these machines, one that I can remember being bought new, in the mid-’70s, one of which I was given, used, probably from North Cornwall!.
The former has bolts, which I managed to get out… eventually. The latter has studs.
Ho hum. I have purchased a bag of 10 5/16 x 1 3/4 BZP “grade 5” (8.8 equiv) bolts for £3.18 from a local supplier of fastners, so they will go in this one, with some anti-seize; I will withdraw them after a while and check to see what’s happened.
I bet the other rotavator’s studs are stuck fast too.