I was timing my '70 472 with a later 425 stock hei and for some reason no longer saw the mark on the pulley with the timing light. I swear this car was timed properly, but it's been pinging and I was tuning it so I figured I'd check. I advanced it VERY much (to the point that it stalled) and the mark came up from below. That mean's it's off by a tooth? Stupid me pulled the distributor out and thinking I could turn the tooth on the distributor screwed it all up. I tried to put it back in the way it was, but all I got was a LOUD backfire after I cranked it. Then smoke and a burning electrical smell. Now I don't know what to do. I read the shop manual and some threads on here, and understand that I need to crank the motor till the pulley mark lines up with the 0 timing mark. Where do I go from there? Could this backfire be something serious?

On my Olds engines with harmonic balancer, The outer ring (mounted on rubber) has slipped and moved the timing mark to the wrong spot. I don't think you have a rubber mounted outer ring though. It does sound like slipped timing chain, the original should have been replaced decades ago. Better go back to basics, take out the plug on the number one cylinder, and turn the crank around till the piston is at the top. The timing mark better be near zero degrees. If that passes, make sure #1 is on the compression stroke. Be sure the rotor is pointed at cylinder #1 wire. Try rocking the crank, watch how many degrees it takes before the rotor starts to turn. 6 degrees means the chain is shot by my thinking. Bruce Roe CLC # 14630

The chain is only about 5 years old with less than 10k on it. That thought crossed my mind, but the things just not that old.

Of course the timing mark is either on or 180 degrees wrong. Try bumping the crank another 1 turn, and set the distributor back in. Of course the timing chain/sprockets could be a problem. Are you sure you have the timing light connected to #1 ?? Just a thought........

I knew that question would come up, I even second guessed myself and checked the book. Front right facing correct? I thought maybe I got mixed up because my v6 is on the opposite, but no.

I guess you could pull the rocker cover on the front side, and confirm the both valves are closed. And with #1 plug out , you could poke something in the plug hole to confirm that the piston is at the top.
Put a chalk mark on the damper at the timing tab for a starting place, install the dist, and see if it will work and be adjustable to run right.

Of course the rotor will have to be retarded from the direction it ends up in when the distributor gear rotates as it goes down in and engages the cam gear and oil pump shaft. Just keep fooling with it, and you will figure it out.

Front right facing correct?

No! Front left facing. I was timing the wrong car! Got it done, just kept missing the stroke. Thanks.