[bbbbbr]

There is a variation on the new-pcb and components approach called the "Ultra Boy Colour" which doesn't require any parts from an OEM Game Boy Color.

It can use a clone CPU that was manufactured (until recently?) for the "GBBoy Colour" (and could also be pulled from the sort of failed SGB-like clone called the "Extension Converter for GB").

  > I redesigned the Gameboy Color from the ground up 
  > based on the premise that it wouldn't require any 
  > components to be harvested from a real GBC, so it 
  > would be compatible with both the original GBC and 
  > clone hardware taken from a GB Boy Colour- since 
  > the KF2007 clone CPU from the GBBC is practically 
  > a drop-in replacement for the CGB CPU found in a
  > real GBC- no software compatibility issues at all.

https://www.reddit.com/r/Gameboy/comments/w0wrt5/no_this_isn...