This is the tank to bowl kit used for the 1950’s through the 1970’s Standard brand close -coupled toilets. Bolts are solid brass, and this would be the one used with Standard’s #5 flush valves as well as the “short shank” Douglas style flush valves. Cushion washer is recessed for the flush valve nut.
Cushion washer has an OD of 3 3/8″, ID is 2″, and it stands 1 1/8″ overall. Remember, cushion washers get squished over time, the dimensions of your 40 year old one may differ.
Brass bolts are 5/16″ diameter and 3 1/4″ long.