Misfires when A/C compressor engages

Check the charging system. In particular, have it load tested for maximum output and especially ripple. If ripple is high and all you can get is one third of its rated output, typically 90 amps, the alternator has a bad diode.

Have checked fuel pressure? Check engine light on?

13.69 volts is just a fuzz below the minimum acceptable voltage. 11 volts is definitely too low. Now the thing to do is to see if the voltage will come back up when you turn off all the loads possible, meaning radio, heater fan, dome lights, etc. If the voltage does go up to 13.75 or higher, suspect a bad diode. It's not very practical to replace them; replace the entire alternator instead.

If it has failed completely and the voltage no longer goes up when the engine is running, suspect worn brushes in the alternator. They can often be replaced without even removing the alternator from the engine. To verify they're worn, use an ohm meter to measure the resistance between the two small terminals in the back. If you get an open circuit reading, irritate the belt a little while measuring. It's common for good brushes to not make real good contact when the rotor isn't spinning, and bumping the pulley a little will create a better contact intermittently so you can take the reading.

Sorry to take so long to get back to you. Just skidded in from the nation's second largest old car show swap meet.

The voltage is still too low but that may not be the reason for the running problem. My first concern is getting that voltage up to where it should be, between 13.75 and 14.75 volts. With the engine running, measure the voltage on the two small wires on the back of the alternator. One will have full battery voltage. The other one will have less but not 0 volts. Use a jumper wire to momentarily ground that wire with the lower voltage. You should see output and battery voltage rise considerably. Don't raise engine speed above idle and don't ground that wire longer than necessary to get a reading. That procedure is called "full-fielding" and is done to see what the alternator is capable of.

If there's little change in voltage when you full-field it, have it professionally load-tested to see how much current it can produce. You could still have a defective alternator with one bad diode.