Like your thread said - weak spark is what I'm thinking.
You've got the air cleaner assembly off when you're trying to start - it's not choking for air, right?
You're seeing gas enter the airhorn assy with manual movement of the throttle linkage?
It's not -25F in Indiana, right?
HEI has an ignition module in it that can need replacing. There's also the coil ...
I'm assuming you've a new cap & rotor.
Plug wires don't arc in the dark and are otherwise in good condition.
The wires going into the cap - what is it, tach-batt and two other wires are solid/no breaks. Check that all those connections/wires are good.
Battery is good? Turning over at a reputable pace? I'm a little stumped if you've fuel/spark ....