if you are hesitant to replace the headset due to lack od experience, consult a bike shop.

if a threaded replacement fork is so long that you have plenty of length to grip the unthreaded Portion with your new threadless stem

Then you can saw off the threaded portion (a saw guide at the bike shop gets the cut square)..

NB: the NL BBB BHP 20 BHP-20 - Headset parts - BBB is a quill based stem raiser.

It Can reinforce the portion that the threads were cut from and potentially take the new threadless stem.
by gripping the upper 22.2 to 25,4 keyed shims, with the stem itself gripping a shim out to the 1.125".

I have used the BHP-21 version in my 9/8" threadless steerer as a stem raiser .. it works well, has for 6+ years.