it is possible to mix and match,, threadless headset, + a 'locking spacer',
in the unthreaded portion.
Then a quill stem raiser, BBB BHP#21 is the best in this application.
As it shifts the adjustment
to the top of a custom manufactured internally threaded bolt .
or, you can use the locknut on the threaded bit,
and do the headset pre load there ..
the quill stem raiser reinforces the threaded portion well ..

a steel tube type stem raiser for 9/8" forks is made also,
quill is in a 1" reduced diameter portion of a steel tube.

then the locking spacer and threaded nut will do the adjustment,
OD at the top is like the OD of the fork steerer... 9/8"

top of the tube.. just put a cork in it.