Very, very many threads on here touch on this subject in depth. So do the various shop manuals, which are cheap, and rather inexcusable not to have if you're getting down that deep into your truck. It is sometimes more problematic to explain something like this without all the necessary context(i.e. your level of experience) than it is to just comb through all of the relevant threads and see what kind of information is already available(in duplicate, in this case)
I'll admit that the search function is a little intimidating at first, but it's the most useful tool on this site(besides the rest of us, heh) once you learn how the filters work.
Simple search, showing only posts with "Timing Chain" in the title:
search.php?keywords=timing+chain&terms=all&author=&sc=1&sf=titleonly&sk=t&sd=d&sr=posts&st=0&ch=300&t=0&submit=SearchPaper manual, *link will decay over time*
http://www.ebay.com/itm/1978-Chevy-Luv- ... 55&vxp=mtrDigital manual, *link will decay over time*
http://www.amazon.com/1978-1982-Chevrol ... air+manual