Stalls repeatedly when cold

1984 Crusader 270.
Some of this is memory from several years ago so may not be 100% accurate.
In 2015 I was getting the boat ready to launch. I had trouble starting one motor, when cold. If I played with it long enough, restarting, playing with choke, etc., it would stay running. I figured it was choke or carburator. Since I have not had much luck rebuilding carbs and since it was 30 years old I just replaced it. Didn't help. Then other factors interferred, I realized the boat wasn't going in, winterized it and forgot about it.
Fast forward to this year: Boat has still not been in, didn't want to let it sit too long without running so figured I would run and re-winterize. Engine would not start. Put gas in carb, would start and run for few seconds. Everytime, but wouldn't stay running no matter how many times I did it. I put an outboard bulb in the gas line and pumped to prime it. It would start, but stall after a few seconds. I discovered that if I started it and continously pumped the bulb it would stay running. Eventually, once it got warm, it would stay running. It now starts without priming it each time (except a push of the throttle, but no bulb squeezing), but stalls after a few seconds, unless I squeeze the bulb while it is running.
It is not the carb/choke (replaced). I thought maybe the fuel pump but it runs fine once warm (including revving up), although it is on the hard so I don't know if it will run full throttle under load. Seems to me if the pump is good enough for it to keep going, and rev, when warm it should be good enough to run it when cold. (of course I don't know anything for certain or I wouldn't be posting).
Any ideas or suggestions appreciated.

you would have been better in the long run to keep the original carb......

Assume you replace the carb.....are the choke adjustments correct? Is the choke coil free and functioning?

did you put the primer bulb in the hose before the fuel pump? If so, you should be able to force enough fuel thru the pump to fill the float bowl in the carb....if you get to that point and the needle and seat are correct, the engine should run for 10's of seconds.....before consuming that fuel....if the choke adjustments aren't correct, they could be the cause.....

I wouldn't jump to any conclusions about the pump until you measure the pressure it delivers.....

restrictions on the suction side (or an air leak) can impact the pump's performance.....

The engine needs to be in tune and in good mechanical shape to assess performance.....and its tough to do that when blocked....

Primer bulb is before (engine mounted) filter, so also before (mechanical) fuel pump.
Didn't time it but would guess engine only runs about 5 seconds (or less) unless bulb pumped (until warm, then stays running).
Choke visually appears to operate properly (closed when cold, gradually opens as warms). Adjusting choke manually, e.g. holding closed or open, does not prevent stalling when cold.
Symptoms not changing with replacement carb suggests pretty strongly problem is not with carb. choke coil was not replaced, but appears to function properly, i.e. it opens choke when engine warm.
Other than choke/mixture what causes engine to run differently when warm? Timing changes with rpm, but not temp to my knowledge. I have had problems with coils, but the problem was when engine was hot, not cold. Plus, engine starts right up when cold if primed. Suggest fuel flow is issue, but supply is fine when engine warm so not likely pump? Could extra fuel provided by pumping bulb compensate for some other weakness/misadjustment?
In interest of full disclosure: both blocks were replaced with remanufatured long blocks several years prior to layup. Both were running fine when hauled except this engine has a chronic overheating problem.

choke moving is good but there are specific adjustments that should be done....vacuum break gap is pretty critical one.

New long blocks - does that mean original distributors were 'recycled'? If so, it would be prudent to make sure the internal advance mechanism is free and functioning and the points are gapped properly.

Being as it has been sitting a while, lots of items could have deteriorated.....probably good to inspect the distributor cap and rotor and make sure they haven't corroded...another easy check would be using a timing light when it first starts up....consistent spark and timing make an engine happy...

You might try putting a vacuum gauge on and writing down what you see on cranking, idle, accelerating, etc. Then do it for the other engine. I'm thinking that you could have some problem that goes away with heat (i.e. sticky valve) or perhaps a vacuum leak that the engine cannot tolerate when cold but can just get by running lean when warm. If both engines read the same with the vacuum gauge (and the already suggested timing light), then you likely will have to start swapping parts with the good engine to find the issue.

On a hunch, and lacking a viable alternative, I replaced the fuel pump. What a PITA that was. But it seems to have solved the problem, so worth it.