UPDATE... I put in the MOPAR vapor canister (confirmed .060" opening on return) with a 1/4" return line to the tank. I am running a mechanical pump on a 440. My fuel pressure used to be 6.5, maybe closer to 6 at idle. Now, I have the pressure gauge jumping all over the place between 4.5 and a little over 6 psi. AT IDLE. As soon as I rev the engine, the gauge settles down to about 5.75. I took the car out for a short run and observed no problem with starvation or power, but I think I am going to consider an electric pump with regulator and return. My 440 puts out about 500 hp and I think I would like that extra safety margin with it comes to fuel pressure. I might add, that I do not just rely on the fuel canister to solve the boiling issue. Recall, I have large headers that run about 325*, or better. The engine compartment on a 90* day cannot get rid of the heat soak from the headers. I went ahead and put one two electric fans with dual relays and a controller that will allow me to set the two fans to come on and go off at any level I chose. More important to solving the temp issue in the compartment, when you turn the engine off, the fans will run anywhere from .5 to 5 minutes. This should be enough time to exhaust the hot air coming from the engine and primarily the headers. I also put a air temp gauge along with Dakota water temp gauge so I can monitor what is happening with respect to air temp at the carb. I will do more evaluations and provide temps and timing in a later post.
Oh, one other thing, on the return line to the tank...i elected to go with a Moroso EFI return adapter that goes on the fuel filler tube. Did not want to cut a hole in tank or sender unit. Seems to work great, especially with so little gas being returned. Should work with an electric pump as well.