340 cylinder head bolts need washers?

My 340 overheated and one of the heads warped. The machine shop says its because whoever put the engine together the last time didn't use lock washers on the head bolts. They said they could tell because the bolts dug groves into the head. Does this make sense? The ARP replacement bolts I ordered didn't come with washers either. My repair manual doesn't appear to show or make reference to head bolt washers.

These are the original bolts.