Washer for certain. This looks like a great project. I did my 66 back in the mid 70's when I was just a teenager. My Dad had three wrecked cars, all 66's, one a convertible. I used the convertible frame because it was made stiffer. We had no powder coating back then. I sandblasted the frame, and for some unknown reason decided to paint it Rustoleum white. (!!!) I was only 15 so that's my excuse. my family had a road building business, so I worked summers in the shop. Had access to amazing tools and shop resources. Anyway, keep us posted - this is bringing back great memories.