Timing chain settings

1999 Monte Carlo 99,000 miles 3.1

my kid was driving it and it started to rap real load and stalled, I went and towed it home. It will start if you hold the gas to the floor. But raps real loud. Sounded like vaulve rap. So I did a compression check, only did 3 cylinders but I had zero thirty and ninty. So I figured timing chain sliped. I opened the timong case and chain has a little slop not that bad, teeth seem all ok. I want to make sure it didnt slip, I found the dot on the bottom shaft, but where is the mark on the top? There are three slotts in the sprocket and a single round hole about a quarter inch round, but no dots, is it the hole that should be at six while the dot is at 12?