| | Re: harmonic balancer
The harmonic balancer on your truck probably fits the 5.0, 5.7, and a myriad of other Chevy engines. You will, of course, only use one timing mark on the balancer.
The easiest way to find TDC, or Top Dead Center, on the #1 cylinder is to disconnect thie ignition coil power connectors, remove the #1 spark plug, and stick a finger over the open plug hole. From there, have someone "bump" the engine over until you feel compressed air come out of the plug hole. Stop there, because you're either right on or very close to TDC now.
Of course, make sure that you don't stick your head, your hands, your nose, your ham sandwich, or anything else in the serp belt or fan while bumping the engine over!
Shine a flashlight down on the balancer, and find the line on the balancer that is closest to 0 degrees on the timing plate (mounted to timing chain cover). If you are @ TDC, your timing line should be within about 10-15 degrees of zero. Use some white touch-up paint to mark the correct line, reconnect the ignition coil connectors, reinstall the #1 plug, and run the engine to operating temp. Don't forget to disconnect the timing spout connector as indicated on your catalyst sticker when you set the timing.