If you have an old school frame with a flat brake bridge like a Raleigh Burner, Robinson, Torker, etc (rather than a tubular one) instead of using a ton of washers why not get one of these spacers similar to what Dia-Compe themselves supplied back in the day.

Machined from aluminium. 

Made in the UK.

15mm (originals were 16mm).

Works on all standard 6mm caliper rear brakes.