My old 1969 WIDGEON had a spinnaker, it was a factory option, however by the time I bought the boat in 1988 all that was still on the boat was the halyard and the fittings on the mast, plus the pole and the spinnaker itself. I rigged the boat based on looking at simillar boats (plus a picture of a 1979 Widgeon) and ended up getting everything within inches of factory original.
First thing, a whisker pole won't really help, it probably won't have the right fittings for a spinnaker (most whisker poles for small boats have a latch fitting on the mast end but a spike instead of a latch fitting on the outer end), and if the boat has a whisker pole the fitting on the mast will be mounted too low for the spinnaker. I know, because I tried to use my spinnaker pole as a whisker pole once.
Rudy Nickerson at D&R Marine can send you the instructions (O'Day Factory original) to install a standard Widgeon spinnaker setup, and he should have most if not all of the needed parts.
If you want to just "wing-it" it isn't rocket science, but another option (contacting Rudy is the most "official" choice?) is the Widgeon Owner's Manual that I created based on the O'DAY original instruction sheet with many added diagrams including those installation instructions for the spinnaker gear. Contact me direct for ordering info (price is still just $10)