I just have some questions on our timing chains. Do they have a recommended KM for changing? Also, if the timing chain snaps/breaks anything like that, does the engine go all outa whack, and kill itself?

 

I would think around the 100K mark one would see a fair amout of stretching, but no necessarily, depending on how the car has been driven. If I had to change out an OPTI, I would go the extra few bolts and replace my chain if it had a fair amount of miles on it.
If they break, its fair to say the unpredictable results may occur.

 

If your going to put in anything other than the stock LT1 replacement I'd recommend going with a double chain and an electric WP, which you can do for about the price of the LT4 Extreme Duty chain. Replacement chains are cheaper, and it get's you out of ever having to replace the ridiculous Opti WP shaft seal ever again.

If the chain breaks things tend to bump into each other. Even with the LT1's massive stock quench, damage can still occur.