Thanks to Bill's Soldersmoke blog for this tip. At the "Dayton" (not actually there any more) hamvention this year, Hans Summers gave a terrific talk about his distain for the archaic NE602 based transceivers and how it's time to upgrade the design using modern methods.
I recommend, grabbing the slides and then playing the Ham Radio Workbench podcast episode. You might like to seek in 1hr 20 minutes to where the talk begins. Hans has also published a paper with more detail.
Hans describes in detail how to generate quadrature signals from an Si5351 clock generator. Great stuff.