A Mighty Vac tool is very useful for not only operating vacuum advance, but has many other uses on these trucks (testing hvac components, cruise control,even bleeding brakes). Good luck
I work at a Caterpillar and Cummins dealer and our parts availability is hit or miss as well. Lots of stuff is USA sourced, but come from states that are shutdown. I don't think this is going to improve until people get back to work...