360 magnum with chevy roller rockers

Pulled the spring, and the check valve/plunger. Went to Ace hardware,picked up some 5/16" lock washers. Mocked it up,until the push rod seat was solid and snug.(against the retainer clip.). Hopefully,the washers don't leave any impression. If not reassemble the internals,re-useable.

Makes sense to me, why the lock washers instead of flat unless the od was an issue?