I am very familiar with the area and Smitty (rodbuildersworkshop.com) has been conspiring to arrange a trip out there this month. March is usually very good if there is any warming trend to make fishing bearable. There are lots of steelhead in the river and the snowpack is huge up on the plateau. The problem is there could be another massive meltoff causing a flood that renders the river unfishable. One year the fish went up the side channels in high water and were cut off. Many of these channels had dead fish all over them when the river dropped, up to 15 pounds. While it was high there was zero angling on the river.
My guess is that earlier is better than later because the cooler weather keeps the meltoff under control and there are less people now than when it warms up.
I am still struggling with a possible flight to the Olympic Peninsula which would put me out of the running for a NY clave. In any case, we can put together a very informative NY page that will get you on the right track for sure.
I think I can arrange for a guide to float you on a driftboat if you fulfill the 'contributing editor' role - take lots of pictures and write up a feature article as a way of saying thanks. Let me know if this sounds interesting to you.
Don't count me out yet, if I don't go to the OP I might have to hit upstate NY to keep my sanity!