need help with a serial diagram and modifying it

hi all I am in need of a little help I am building a Cat cable for a yaesu ft-757gxii transceiver and the diagram has me a little stuck so I am hoping some one may have a moment to help me I have never worked with serial before other than making straight cables. based on the image I am including the 2 circles resistors are the pull-up resistors correct? I want to replace the transistors with 2 pc123 opto-isolators but I am not sure what I have to do to do that with this circuit. now for the hard part that has me confused the most on this radio RTS triggers another circuit for the transmitter but I notice they have it tied to the incoming serial line can I still use RTS or will I have to build a separate circuit?

Thanks,
Yonu