I know a 255 LPH Walboro is what the Mustang guys use. IIRC Those Ford fuel injections run at 30 PSI stock. The 5.0's may run a bit higher... There might be a possibility of running a high GPH high pressure pump like what Aeromotive builds. They may provide enough suction to not stress the pump much, but that's an expensive venture if it fails... An in tank Walboro 255LPH is about $60 as a replacement for a stock Mustang pump.

The stock pumps are rotary vane pumps, so it may draw fuel just fine, but it also probably will burn the side pump up from working so hard... Walboro does make a 255 LPH pump for in line applications that will provide the correct pressure, with the cost around $100 IIRC.. I know while I was in the local Napa 1 day, there was a guy with a GM bread van in the parking lot with a dead fuel pump. His company couldn't get there for a while, so he bought an external pump that would work, and wired it to a switch directly to the battery, so he could finish his deliveries