Now, we need to make sure that this isnt being caused by the fuel system(just to get it out of the way). What you need to do is, spray some engine start fluid into the manifold and then try to start it. Pay attention to how the engine responds to the fluid. If it sounds like it helps, then we can get it out the way. If not, then thats what we need to focus on.
I was just wondering, if you have a timing light? with a timing light, you can check if there is spark when the engine is giving up. You would hook it up the same way as if you were to check timing, but you wouldnt be interested in the timing. You would just watch for the flashes.(its ok if not available)
also, after or before you do the check with the engine start fluid. Check for vacuum leaks especially around the intake manifold and throttle body.
I was also wondering, if you checked the electrical connections at the ignition coil, distributor, and alternator?if not, do so.