273 Engine will not start - Ideas?

My 2 cents

Maybe it has good spark. Just because it popped a couple times doesn't prove it to me.
Buy an inline spark checker so you can see that. Charge the battery up too.
Popping also could be intake valve not shut when the spark fired.
10* BTDC at 600 rpm should be fine but not sure what engine work etc could have bumped the dist.
66 273 has a solid lifter cam. Valve adjustment is another possibility for not seating in time.
Later Timing chain cover. So what is being used as the zero reference for the timing? Or is the correct cover and tab now installed?

Since the plugs were wet, lack of fuel does not seem to be the issue. More likely the opposite.
Carb. Not understanding pushrod comment.
The small block fuel pump needs no pushrod.
In any event the question is whether the correct amount of fuel is being supplied for starting cold.
For starting fuel is drawn through the idle (and transfer ports) by the low pressure created when the pistons move down and the air flow through the carb bores is restricted by the throttles and the choke plate. We can add an additional shot through the accelorator pump by moving the throttle.
> If you see fuel squirt out of the nozzles when working the throttle, then there was fuel in the accelerator pump and that came from the bowl. When a car sits for a while the intake manifold dries out. A few extra shots are often needed so under vacuum there are enough vapourizing fuel to rewet.
> If the boosters are wet, then the fuel level in the bowl is too high. If the boosters are dripping the fuel level is too high. If its coming out the vent, its way way too high. A fuel bowl that is overfilled will contribute greatly to flooding.