It turns out that the gas tank filler necks across the various models of Virago are similar enough that the caps are interchangeable. Sort of. The standard flip-top cap will click into place in the under seat tank if the neck hasn't been bunged up too badly. If it has, one must obtain Yamaha special tool, # XV535-GT-RT-O1, or gas tank reshaping tool #1.
And here it is:
Whatever, it works. I also removed the remaining pint of gas from the tank and while the engine would run on it, it smelled a bit gamy. Fresh gas and I'm pretty much done. Got the plate and insurance so now it's off we go.
My variation on the song is that the motor sounded fine until it quit running with a flattened battery after 2 miles. The charging system is still not working.