I power washed mine as well and scrubbed hard with a brush and Simple Green while concentrating on the "corners". I agree that mine does not need clear on the box. Be careful if powerwashing on concrete, it will scar the box if it moves around. Most people blast the sheetmetal parts and repaint as appropriate. Some high enders zinc plate brackets flap doors and clips. I am going to paint mine.

Make sure if you aren't positive of it's condition to get the heater core checked out. Rivets for the brackets you drill out will be different and many suggest a washer so they won't pull through the fiberglass

I am about half way through mine right now and need the stamp as well. I was going to do with out but if it is available and reasonable, I'd love to hear the source.

PS, you didn't damage the blower motor taking the fan off did you ? I did, and it is not a cheap lesson.