What’s the difference in bearing cup dimensions from the old 1” threadless and a 1” threaded setup?

Why can’t this be done… longer threaded fork steerer tube, section of 7/8” cut quill stem stuffed inside and tack weld/plug weld under the top bearing cup, grind down a star nut star or weld a nut in the 7/8 quill tube, then just use a 1” threadless headset?

Admittedly a lot of work, but would the dimensions work?