Fixing one thing leads to another...

[jhv48]

Before you start chasing your tail any further remember that California is currently pumping their winter blend of gasoline which has a lower boiling/vaporization temp than summer grade gasoline does. And with the unusually hot temps we have been experiencing this winter it could be that the winter grade of gas and your increased engine temp have created the perfect storm to cause fuel percolation upon shutting down of your hot engine.
If it were me, and I think the oil thermostat is a good idea, I would install a 180 degree thermostat. These cars were designed in the 60’s, when fuel percolation wasn’t a concern. And with the advent of highly pressurized fuel injection systems, calif can run their highly volatile blend without any problems.
But our cars can’t handle the low boiling point.
You can wait till summer and your problem could go away. Summer blend is much more heat tolerant than winter blend. But then it may show up again as soon as we switch back to winter blend.