Its a special socket called an "oil pressure sending unit socket" - seriously. I wanna say its 1-1/4 but I dont recall offhand.
I bought mine at NAPA but you can rent them from advance auto too I think. Its just a deep 6 point socket since Ford went out of their way to cut the corners off the sender unit so that a typical 12 point deep socket doesnt work.
Just use vicegrips or channel-locks. I broke that post off that the plug hooks up to, and used some channel-locks on mine. You said you're replacing it anyway right?