All you need is simple serial comms, simply connect the pins together and connect them to a pull-up resistor. Set both pins as inputs, the pull-up resistor will cause them both to read HIGH.
In order to send data make one PIC an output, and set the pin LOW, this is the start bit for the serial comms - carry on as normal sending the byte just like RS232, ending with a stop bit (setting the pin HIGH again, then TRIS'ing back to an input).
The receiving side simply waits until it gets a start bit, then does the normal serial receive routine.
To transmit the other way, simply reverse the process!.
There's no need for Manchester coding, it would provide no functionality whatsoever, and would slow things down.