pcb , you're right, no washer in between, and I remember now there were two in the bag I provided them. He said, "Not sure what these are for, but I can figure it out once I get into it."
I think your assessment is spot on that they knew they goofed. When I picked it up and asked how it went, he said, "Well, we had a hard time with it. These old frames are extremely hard metal and difficult to cut." These guys were very young so maybe this is the first time they've even touched or seen an 80s frame.
Interesting idea about taking some metal off the top headset lug, but given my luck thus far and lack of knowing any good mechanics in LA (I'm sure we have them, I just don't have any good leads), I'm pretty reluctant to take it to a shop again.
Thanks for the tip on the Tange Passage. I will probably try riding it once the bike is built up and see how it goes, and it it keeps coming loose, maybe swap for the lower-stack headset. If I did that and found it needed a spacer just to raise it a hair, where do you find keyed spacers? The only one I found was at Rene Herse:
https://www.renehersecycles.com/shop...adset-spacers/