I know about two, both are weekly.

Black Rock Coffee - Hosted by the NW Mustang and Classic Fords club, I believe it's 8AM every saturday at 136th and Mill Plain (Safeway Parking Lot, you can't miss all the Mustangs clumped together.

Beaches Cruise in at Portland International Raceway. Every Wednesday at 4pm(?) they have drag races and music as well as a nice show of cars. The website says 74 and earlier, but they let Foxes in. It's like, $5 for the driver and 1 passenger, children are free. Proceeds go towards various causes. They put us in the Mad Max section:

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Anyone know of any other cruise ins in the area?