What do the SBC-based 4.3 and LS 5.3 in my Safari and my dad's Silverado have to set their timing?

I know the Vue has a chain. I only know this because my mom's Vue closed in on 70k and I started getting concerned about a timing belt snapping and destroying the engine.

But, I've never head of having to change anything on a SBC or LS motor.

OHV motors for the win, I guess. Since they seem to be the most maintenance free.