I looked through what I have on Dowty but as expected not a mention of thread type anywhere. Diameter yes. TPI, no.
Nevertheless, as Dowty were an aviation firm that initially made their name with internally sprung undercarriages and the Dowty Tele fork was their sole try at anything motorcycle I would expect them to use the taps and dies they already had in their factory so far more likely be BSF
, not cycle thread.
I expect you can confirm this by measuring other threads on the forks. Nothing 1/4” of course as both 1/4” BSF
and Cycle are 26tpi but what about the steering damper rod. From memory that is 5/16” so should be the same diameter as your problem butchered bolts.
Having said all that Dowty being aviation based can spring funny surprises on you as the aviation world sometimes liked to use non standard thread pitches to ensure only the right quality of fastener was fitted in sensitive areas. It pays to check very carefully.
Sorry I can’t do any better. I have careful instructions on care and maintenance but no actual advice on what thread form.