Gerry Butler made them specifically for LF sheet development. I would not classify these as DIY, rather DIH (did it himself). He bent the SS wire around forms and soldered them in sizes from 4x5 to 11x14, until his hands became too arthritic. He was already retired when I bought mine (2 – 5x7) out of his remaining stock 10 years ago.
Congratulations on the find, they are the best of the slosher–basket designs.
BTW, when using pyro developers (possibly others as well), you should be using a developing tray one size larger than the basket and not skimp on developer, for even results.