For CLD-2080 you should be able to use CLD-3080 SM. I have the ProScan clone SM of the CLD-2080 though.
Yes CLD-D504 has what is called "recombined composite". You can bypass comb filter in CLD-D504. It is CXD2023Q. Datasheet for this IC (not SM) shows same info on Pin 71 as the post here:
https://forum.lddb.com/viewtopic.php?p=98007#p98007 so you could then make a custom S-Video Y -> Composite cable or tap R145.
Regardless of picture, CLD-2080 is much better built than CLD-D504. Video quality of CLD-3080 though is a jump up from CLD-2080.