Problem solved. I opened up the distributor cap to see again if there were any loose wires and I noticed quite a bit of free play in the rotor - turns out the distributor wasn't properly seated. When I was taking out the Pertronix, one of the little bolts had fallen in near the vacuum advance, and I had to take the distributor out and turn it upside-down to get the bolt out of there.

Still don't know why the Pertronix didn't work - I didn't take off the distributor until after I'd installed it and tried to get it working - but that might be something I try to figure out tomorrow. Phew! I was worried that I somehow had fried my fuel injection system with the Pertronix.