4 vent gas tank.

Drive faster.Heh heh.
-Seriously though; if you defeat or partially defeat the vapor separator, you can do anything you want to. However the returning fuel which is above the liquid-line would tend to aerate the fuel, and possibly increase the vapor pressure in the tank.If you fully defeat the vapor canister(not recommended), you will need to vent the tank in some other way, else it might balloon in the hot sun or implode on the highway or otherwise give you operational fits.It might be possible to hook one of those tubes through the sender hole, and bend it down.
-Honestly though, modding the sender to accept a return-line is not that tough. Or you can just trade yours for one that is already modded.
-Im guessing your car is experiencing vapor-lock, or similar symptoms. I heard big blocks sometimes do that. Never had a problem like that on any of my LAmopes.