First of all, it's nice to see a younger person taking an interest in a 69 Cadillac. It sounds like you already have begun teaching yourself how to maintain the car.
You will find that we are willing to help. That 472 engine is a strong motor, and when tuned correctly should run very well.
If the timing is too far advanced, the car will ping, and also suffer from pre-ignition, which is the engine continuing to sputter and run on after you turn off the key. For a short term fix, keep the car in "drive" when you turn it off while you are looking for the cause. Don't let it cough and carry on for any longer than you need to.
Now you need to figure out what is going on.
In setting the "base" timing you need to remove the vacuum from the distributor. You can plug up the vacuum line with a golf tee, or small bolt.
Set the timing to spec. Also observe if the mechanical advance is working. When you rev the engine, the timing mark should change. Maybe yours is stuck in the advanced position.
Another likely source is excessive carbon on the tops of the pistons. I used to use GM Top Engine Cleaner, which is poured through the carb. I don't know if this stuff is still available, but you can probably find something similar in a good auto parts store.
What I used to do with this magical stuff is dribble about half of the can through the carb, raising the throttle to keep it from stalling. The taking the 2nd half of the can, dump it in to the carb, choking the engine out. Turn off the key, and wait 15 to 20 minutes. Then start the car. You will see horrible smoke coming out of the exhaust, and what you need to do is now take the car out for a nice run, about 20 minutes or so, and beat on it a little. You will have blown out a lot of carbon and old varnish, and the car will run much better.
Then put a little dab of grease on the back of the gas pedal where it rubs on the metal lever part of the throttle linkage. At this point, it will feel like you took 40K miles off of the car, providing everything else is tuned properly.
Let us know how you make out.