HP 4600 Printer Question

I have the basic HP 4600. I was told by a non-HP service person that all
the duplex hardware was present in the basic machine. Looking at their
copy of the service manual, it appeared that the only difference between
the 4600 and the 4600d is the main PCB (Formatter) that memory and I/O
modules plug into.

If I were to purchase the Formatter for the duplex version of the 4600,
would it turn mine into a duplex machine, or would I be wasting my money?

Fred