I never made something like this, but in theory, you just need connect the midi out of sync sender to midi in of sync receiver, 2 midi-usb devices should do the work, you may need a Dim5female-Dim5female adaptor if both midi-usb devices have male connectors.
I think you can do this in another way, connecting serial to serial ports of PCs with a cross-over serial cable, and installing midi to-host drivers on both PCs, then serial ports will act as midi devices. You cant connect common midi devices to serial port this way, just devices with midi to-host connection, because common midi and midi to-host baud rate arent same.
