Joe -
Chinook can certainly be taken on a fly. At various times I have target them with some success. Over the last 30 years I have formed some opinions on methods are consistently succesful -this includes:

1) Fishing on a swing ala steelhead is not a productive method for chinook.

2) Flies - succesful patterns fall into two groups - are small, dark, buggy -typically size 6s and 8s varying in color from dirty orange to black. Have noticed that successful colors vary from river to river so experiment. The other approach is a baitfish type bug fished pretty aggressively.

Have had success on traveling fish - I prefer to tagrget fish in the estuary or the traveling fish up river. This is particularly true here in Washington where if you are fishing waters that are open for chinook you will be dealing with lots of gear guys which will limit your access to fish holding in the deeper stacking pools. There will be either guys fishing on top of the fish or the boat traffic will force the fish in deep/heavy water that limits the access for the fly angler.

The Skagit fishery is likely to be really popular with the gear guys. With this year's snow pack I would expect you will be dealing with clear water and lower flows than normal. If I were to target chinook I would fishing a traveling slot that affords a chance to get my fly to the chinook's level at dawn or dusk.

The tackle that I use for steelhead has been adequate for those chinook I have caught,

Tight lines
S malma