Hello Mark and welcome to the HP Forums!
I would love to try and help with your duplexer questions, but I do need a little more information. What is the rest of the product number for that duplexer? Depending on the final numbers of the product number (e.g. C9101A-001, C9101A-004 C9101A-015, etc.) the product could be compatible with a number of different units.
Another route to narrow down the selection of printers the duplexer is compatible with would be to visit the HP Parts Store website.
Please let me know the results of what you find. Thank you for choosing HP Forums!