The "field engineered" RE Bushing with locknuts is, IMO, a better connection than RE washers.
I employ this little trick regularly when connecting motors, which often come with holes (not KO's) that are larger than the size of the conduit I'm using.

Was there a reason for using a 4-11/16 Box rather than a 4"? (The covers are so much easier to get!) [Linked Image]