this is good Six Pack, but the washers are coned/domed for a reason. That reason I believe is to keep the bushings cupped in their positions. I should have made many of these when I made mine years back, but if you search on this long read, IIRC, I explained how I made my coned/domed washers out of aluminum.
IIRC, I placed the over sized aluminum washers over an open round cavity and blew at it once or twice with a rubber mallet and a shaped wood chuck to act as the male.