Issue with running a carb tank on efi is that a carb car can not have fuel flow for a second or two in turns and the engine wont notice since the carb has the slight reservoir in it. An efi car will loose fuel pressure instantly if the pump sucks in air. The baffling/"can" in the EFI tank keeps fuel where its needed during accel, turns, and breaking.
Many wagon people will swap an astrovan efi sender in the stock tank (without baffling) and its mostly OK but that is due to little to no options for EFI tanks on those cars. A wagon tank is taller and narrower than a coupe tank so the fuel doesnt slosh around as bad.
I ran an external fuel pump on my LS car with stock sendor and carb tank and below 1/3 tank it would suck air and loose fuel pressure. The coupe/4dr tank is so flat and wide that a little sloshing can expose the fuel inlet easily.
The efi tanks new are so affordable (a lot of the time under $150) and most old tanks are bad enough anyways that the tank is an easy decision to replace. I think I got my fuel sender off rock auto cheapest, the tank off some ebay seller for like $65 with shipping during their 15% promo they had last year and a walbro 350 in tank pump cheaper than it would have cost to go with a good external pump and a fuel mat that goes in the tank like the holley stuff mentioned earlier.
