Those serrated washers (along with 5/16" bolts) were also used on the '55 car door and hood and fender mounts at some body plants where there was enough left-over bolts and washers from the previous year models.
In '55 and '56, those serrated washers were only used along with a nut to mount the hood hinge to the cowl (4 required per side). In '55/56, the doors hood and fenders used the new serrated 5/16" washer/bolts that look like a flying saucer.
Once the body plant(s) received shipments of the flying saucer bolts during the '55 model year, they quit using the serrated washers and separate 5/16" bolts and substituting them for the flying saucer bolts (except kept using the serrated washers for hood-hinge to cowl mounting only).
As far as I know, the separate serrated washers are not reproduced by anyone, but you can get semi-duplicate repro's of the flying saucer bolts from some of the repro parts suppliers and use them instead of the separate washers and bolts, but it wouldn't be period correct on a '54 Ford. Also the repro flying saucer bolts don't look exactly like the originals.