Also, have you ever attempted to measure the amount of slack in the timing chain?

Basically, turn the engine in one direction, stop turning when the mark on the harmonic balancer is about to "fall off" the timing tab. ( basically it means to turn the balancer until you almost run out of marks on the tab.) Then have a helper watch the rotor while you turn the crank backwards from the previous rotation.

Once the rotor starts turning, stop and count the lines on the tab. If you get more than 2 marks, consider changing the timing chain and gears, if you get 5 or more - don't hesitate, change the chain and gears.