Timming chain

On my 82 gmc 1500 if the timming chain is gone would the timming marks still be pretty close to normal?Is there a way to find out if it skip or if it stretch without taking it out?The engine is a 350 with 140.000 milles it runs very bad and have no power at all it pings alot like the timming gone way out of place.I think that it could be cause by the electronic control module (ecm)is that possible.I remouve the cat in case it was plug up it dint help anything but I had trouble with the ecm for a while I had to beat it up when the truck stalled or dint want to start.
Thank you in advance for any reply guys.