I have the datasheet of the PL-2303HXD but I'm looking for the Reference Design Guide from Prolific. This PL2303HX Rev D is without crystal, it's very interesting for a very small design. Have you this pdf file ?
Attached picture shows the actual reference circuit for PL-2303HX Rev.D chip, it's a part of GPS module USB interface circuit(GPS RX,TX signal to USB).
My previous reply showed a actual design for USB GPS receiver, I bought 10 pieces from online shop(taobao.com), assembly them on my PCB according to my circuit, they can work normally.
More detailed infirmation for reference design refer to attached document.
It's helpful for your design.