Good to hear that you are optimistic for success after removing the gear and test fitting the clutch. My vote would be for milling the gear as opposed to the washer. I’ll throw out this relatively affordable option as well and especially since it gives you the ability to make a “best offer” https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/153541363875. I bet you could have it in your hands for $15, maybe even a little less. Of course some people like to work with what they already have and if you have a good relationship (or are cultivating one) with a machinist then maybe that is the best option for you. If you need a measurement of the gear to give to your machinist then let me know and I can provide that for you.