[RWebb]

Special interest vehicles must be maintained as a collector's item and may only be used for exhibitions, parades, club activities and similar uses, but not used primarily for transportation of persons or property (see ORS 805.210, 805.020, & 805.030)

note that the law does not say recreation or pleasure driving - but I agree you can surely do that w/o much worry

also, PDX has red light cams (IIRC, it is the only Orygun city to be allowed them) - so if the cam 'sees' no front plate they could potentially hunt you down and the hassle you to explain why (the hassle might be to prove you are legal by making an in person visit to DMV or something)