If you are getting a good strong spark, then you should get combustion when you dump fuel in the throttle body.
But if you have a bad or wrong coil and a weak spark, it might not spark well under compression in the cylinder.
If you've got good spark, it should fire when you dump volatile fuel in the intake.
Do you have a points gap (about the thickness of a business or playing card) at the cam lobes? (I assume you do if you are getting spark when laying the plug on the valve cover.)
At this point, if I were you, I would probably try dumping some more fuel into the intake. The plenum at the bottom of the manifold is the full length of the engine and about six inches wide. So it can hold a significant amount of fuel to make the vapors you want to burn. Here are a few pictures that might make you feel a little more comfortable about dumping more significant amounts of fuel in the throttle body.
Just the top half with intake ports:
Bottom piece connected to top with 8 rubber gaskets, showing the large throttle body hole in the center. You can see how this can hold plenty of fuel: