Akguy,
Frankly, the hardest part of timing these engines for the uninitiated, is finding Top Dead Center. I'm sure a search on this site would reveal better instruction than I can give, but what the heck - I'll jump in.
The "timing window" that Denny is speaking of, is low toward the rear of the passenger side of the engine. Silver-dollar sized hole, with a pointer in the middle of it. At TDC, there is a mark on the flywheel that will show up in that window, assuming it's not totally covered by grease or dirt. I believe the timing mark you're looking for is a bb (you know, a round ball) which is recessed into the flywheel.
So how to turn the engine to get it lined up? First, remove all the spark plugs to relieve compression and make it easier to turn. Second, know that the engine turns clock-wise as you face it from the front, ie: staring at it between the headlights. Third, be sure the truck is in neutral.
Now - some people speak of using the starter to "bump" the engine over to find TDC. In my experience, this is a very imprecise exercise, and it moves too fast for me to follow. So try this: standing on the driver's side of the engine, use your right hand to push hard against the fan-belt to maintain tightness, while using your left hand to pull the fan toward you over the top. If you can keep the belt from slipping, this will turn the engine.
If this doesn't work, I suggest borrowing/buying a hand-starting crank. This fits into a whole in the harmonic balancer, and allows you to turn the engine by hand (it will only turn in the proper direction). Not sure if NAPA or such sells them, but Jim Carter and Chevs of the 40s probably do. It makes turning the engine for timing rather simple.
Finally, the engine can also be turned by crawling under the truck, removing the flywheel cover behind the oil pan, and using a prybar on the starter ring teeth to turn the engine. Easier with 2 people, and still awkward, in my mind.
NOW - how do you know when you're close? Well, first off, know that there are 2 Top-dead-centers. That is, the piston for each hole is at TDC twice for each complete cycle: once is at true TDC, when it fires, and once during overlap, when the valves are opening and closing.
So once you GET the BB lined up in the window, there are 2 ways to know if it's the right one: The first, is by pulling the distributor cap off and seeing if the rotor is pointing toward the tower leading to plug-wire for number 1 cylinder. This assumes the engine was at least close to set right when you started.
The second way to know is by watching the valves for number 6 cylinder (rear-most 2 valves)as you turn the engine. Turn the engine until you see the #6 exhaust rocker arm push down (that's the farthest one back). Start turning slowly at this point. Now, watch carefully for the #6 exhaust valve to just start to come back up, and at the same time, the next closest valve, the #6 intake, to just start going down (or opening). When this happens, you are very close to TDC for the number 1 cylinder. Keep turning in very small increments until you see the BB in the window.
For what it's worth, this is all MUCH easier with another person helping. And, I wouldn't panic if you just slightly pass the pointer - if the BB is in the window, at all close to the pointer, you're close enough to get it running half-decently.
Once you're confident you've found TDC for #1 cylinder, you can adjust the position of the distributor to be just opening. I can beat that to death next, after you've found TDC. Post back with your progress!
-Michael
