Yesterday it purred. Today it pukes at partial throttle.

Try disconnecting the vacuum advance hose and plug it. Then try driving the car. If it is now ok, change the distributer pickup coil. At idle there is no vac to the dist. As soon as you open the throttle vac is applied to the dist, and the pick up coil rotates, there could be a issue with the coil electrical circuit that shows up when the pickup moves. By removing the vac hose, you are testing this as no vac is applied at all.