I really doubt they're similar, but I recently took the cylinder out of a '98 F-150. I had to install the key, then push a little metal button in and the cylinder pulled right out. I know that most of the time removing the cylinder requires the key be installed, but I'm not sure on an '81.

'91 LWB, 31x10.5s, KYBs, A/T "I look like Robert De Niro, I drive a Mitsubishi Pajero" - Billy Bragg (not the original lyrics, but that's how he sang it when I saw him in Dublin in '04)