[AZKen]

Does it also squirt after sitting but before trying to start?. If it squirts, pump accelerator more and faster than you have been while cranking starter.
If in both cases you mention, carb squirts a good stream, then I lean towards timing. These motors do not always run good at the "book spec" timing. Advance/turn distributor, in small increments each starting period to find good results. Obviously if it gets worse, then retard. This may take weeks. Don't rush, let it sit same period of time or the experiments will be misleading. The fact you say an electric fuel pump made no difference, points to timing/weak spark also. Notice if distributor turning helps the after-sit starting or stumble...or both.

More info and your test results may change my mind.
The only carb issue could be a a sticky needle valve, but again you say you have squirt in both cases. So that means there is gas in the bowl and motor should at least fire pretty quickly if choked.

The starter fluid is a little stumping. It is highly combustable. It could be too cold to start otherwise and then when warm it is OK.
Can you advise:
1. After sitting does starter crank slowish?
2. Does the motor not even fire or pop or almost start ....without fluid?
3. Have you checked all vacuum lines?
4. Have you tried squirting gas into carb instead of fluid? Like a good shot/mist of gas from a squirt bottle.
5. Gotta block warmer?

Another cause can be timing chain stretch???? Not sure if that fits this.