Timing is a little odd. you can do a search to find better info, but here are the basics:
The timing marks are on the flywheel - you'll want to use your timing light and line up on the dot (or BB, as it is sometimes called) not the line. The line is TDC, the BB is 7 degrees ATDC (I think...) there is an inspection cover just behind the dist. that you use to look for the timing mark (it's not on the pulley like a lot of cars)
If you can't see the marks clearly with the timing light, you'll want to pull the inspection plate - which is under the truck, between the motor and transmission. you'll have to hand turn the engine, or use a remote starter switch to bump the engine (make sure the coil is unplugged) and get yourself a little white paint - testors or something - and when you find the BB and the TDC line, mark them - then start the process all over again with the timing light.
Again, do a search on this - there's a good thread from a few months ago about timing in this section.
But the most important thing, as 60wag mention, is getting that dist. to engage the oil pump. If you get that wrong, your oil pump won't work and the engine will seize. It won't run more than a few miutes like that.
