Now hold on there; That is not likely to be a plug issue.
How long has this been going on? Oh, since before the new plugs went in;I see.
When a cold engine starts right up, and idles smooth, it means the plugs are working,and so is the choke and so is the carbs low-speed circuit.
The crappy hot-start is usually a carb issue, but if you have a slanty with solid lifters,the long crank time could; that's could, be related to tight valves.So you always have to eliminate that first. You could spend hours dinking with the carb, and never see an improvement in the hot-start, until the valves are adjusted right.
So after they are known to be right, I always do a compression test. In this way I know what to expect.If it's good, I know I can get rid of the hot-start issue, easy.
But if compression is sour,and i'm working by the hour,there's not much point in continuing.
So after the valves and compression are known to be good, then we can attack the carb, where the real issue is.
So you are down to two issues;
1)the long crank time when hot is usually from A)the fuel either not being in the bowl, or B)the fuel being puddled in the manifold. and
2) the stalling when going into gear, is usually an air velocity issue..
But first, let's go back and make sure the valves are adjusted right, and that the symptoms persist.
So after that, and that the problem persists, here's my thinking.
Since the engine starts nice when cold, that means it had fuel in the bowls when you shut it off.So that rules out 1A, leaving us with 1B). Fuel being in the manifold is a flooded condition. The usual work-around is to put the pedal to between 1/2 and all the way down and simply holding it there while cranking. After a few seconds the engine clears out and fires right up, and you can take your foot off the pedal. If this is how yours is behaving, then we will have to determine why it is flooding.
More to come....