RTS/CTS Protocol for UNIX 4.0

[utzoo!decvax!duke!chico!harpo!vax135!houxi!ihnss!eagle!mhuxa!mhuxj!bwkna!mhexa!bis]

Does anyone have a modified 4.0 tty driver that supports a
Request to Send/Clear to Send protocol over a DZ?
The DZ ties RTS to DTR and ignores CTS, but it is possible
to make a special null modem so that the terminal's RTS lead
comes in on the DZ's CD lead and the DZ's DTR lead goes to
the terminal's CTS lead.
Does anyone know how to do this?  The equipment I am using
(half-duplex stuff) does not support XON/XOFF.