There is Another Way.
Why
convert from another obsolete standard (625)
You can
generate 405 line composite video directly with a graphics card in a PC and a handful of passive components to mix the VGA R G B and sync signals. Then you will probably need a System A modulator, I use this one
https://www.earlytelevision.org/405_modulator.html
here it is in action
https://youtu.be/ahzdx4KgWBg