I helped a friend put inverted WP forks on his '83 Maico 250.
We pressed out the Maico stem and the KTM stem (the WP forks were from a mid-80s KTM 250) and had a machinist make new stem that copied the Maico dimensions for the bearings and length but also fit the KTM triple tree. Then I machined a set of steering stops for the lower stem and bolted them on. We pressed it back together and bolted it on the bike.
But I agree, don't bother. We did it because he had the parts, the Maico has a front drum (the KTM had a floating disk), and it was cheap. And it's a Maico, i.e. a collectable machine (the old parts are in storage).