Well I have to say I've never seen a fuel system actually drain a carb to the point the pump has nothing to pump myself. You say that you have and I will not dispute you on it.
I wouldn't remove a fuel return.
IMO, If the tank is building vacuum I think I'd look for a plugged vent. I've heard stories of spiders nesting in vents plugging them. Never experienced it. Maybe even running the cap loose can help determine.
Vapor lock can be due to too much heat running through the crossover if it has one. Excessive under hood heat too. Maybe even low fuel pressure. Is it percolating the fuel after shutdown?
Block offs for the crossover can help. Heat deflector plates and fiber carb spacers are available. Then there's always the cool can option. A little extreme for this though.
Just what is the vehicle and engine. I think I still have an '89 Ramcharger SM around here.
I am familiar with needle and seats and yes it can flow fuel by the needle and seat I have seen it many times .I had the truck quit and when I pulled off the fuel return it shot out a stream three feet till the pressure bled off.. Why is it vapor locking and . and can I remove the return. This is the first 80s dodge I have owned and none had the return. Did I forget to say I too am a mechanic I have not run into this problem before with a dodge and there have been many pickups and cars.