I puting in a 351 and wanted to keep the electric in tank pump. What I did was I found the fuel relay underneath the seat and found the hot to the pump, I think it's pink with black stripe and ran a hot from the fuse box from the radio fuse and mounted a switch hidden in the glove box, works great and if I was in an accident the inertia switch still works. Just find a place that's not so obvious and not under the steering wheel, the first place someone will look for a cut off switch.
Good luck!