The only reason I can think of to use washers here would be to use locking washers, but if you’re using Nyloc nuts that is superfluous. Unless you see them in the parts manual I wouldn’t consider them.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
3
Definitely no washers under the bolt heads, as that would mislocate the shear load on the bolt shank. Can’t recall ever seeing washers under the nuts. I think in general it’d be a bad idea, because the bolts are hard, the nuts are hard, the flanges are hard, but a washer might be relatively soft and cause the attachment to loosen under load.