update on my end, Thanks to help from @Cereth with graciously providing reference harnesses (and gentle prodding and reminders), This is the next mass-produced project I have on my bench
This will be a full kit, meaning
Serial cable - 4 ft (605-022?) (thank you for the pinout above, @twistedsymphony!)
Home button harness (605-0226)
Length wise, this should help out with the peeps who have the card reader in the center of the cabinet, rather than right on the CP.
I also have a harness that plugs the card reader into the button harness with a pass through (605-0229) but given that I'll be including the Serial cable itself, I'm not sure that's needed.
I will be making 50 sets.
I'll try to keep the cost on these as low as possible but damned if the connectors aren't as rare as hen's teeth, it seems.
I'll definitely take at minimum the serial cable.
Might take a whole set depending on price.
Thanks for getting back to this one, really appreciate you.