Great job. Holes don't look bad at all. Should bolt up nicely. Washers can be used to spread the clamp force if you wish. Washers are not always required. They should be used under the turned element. (nut or head) They are used to prevent galling sometimes and on enlarged holes. There no reason not to use them in this situation. I always use them under a lock washer. Follow correct torque values for size of bolt. Bolts are equal to, or stronger than, rivets and way cheaper for all of us who don't have rivet tools and torches to heat these big, carbon steel, solid rivets.
I use rivets all over the place to fix a lot of things but they are smaller pop rivets. I like rivets. I have a pneumatic hydraulic rivet gun. I riveted new seats and deck on an aluminum boat a month ago. I don't hate rivets. I designed with solid aluminum rivets for 40 years....and spot welding and bolts. They are the correct technique for a totally authentic restoration for sure. They have almost faded away in building and auto construction.
