I've caught 3 & 4 pounders, in the Long Tom. That river is just one of many tribs that, feed into the Willy. So, there should be some larger fish in that river too. I would think that, there would be even bigger ones as well. The state record, is just a tad over 8 pounds (record caught in Henry Hagg Lake).
Also...according to "The Complete Angler's Guide to Oregon", by John Shewey, the best stretch is from Minto-Brown Park south to the mouth of the Luckiamute River. So it sounds like, that's where your best bet will be. "Fishing in Oregon", by Maddy Diness Sheehan, states that smallies [in that area] are found primarily at the mouths of sloughs...and the edges of main current. It also states that the largest fish are taken, in early Spring (March & April). But, that doesn't mean that you still can't find some--before the water temps drop too much.
Good luck; and let us know how you do.