Backing plate bolts too long?

[Zephyr4]

I'm putting my rear brakes back together and I'm finding that the backing plate bolts seem to be too long on both sides. The car appears to have been in a barn since the 60s until I bought it so I don't know how it rides or anything.

So, maybe something is missing or maybe there are incorrect parts being used.

If I tighten the nuts to just 30 ft lbs the hole for the pins is above the crenellations on the nuts:

20180611_132930.jpg

The bolts are 1 9/16" long and the nut is 5/8" in total length.

20180611_132951.jpg

Do the nuts and bolts look correct? Am I missing a washer somewhere?

I've looked at the exploded view in the Snyder's catalogue and can't see anything I'm missing.

Can I safely add a thick washer under the nut?

(This is a '31 Tudor.)