1984 ignition cylinder...how do you take it apart?

[72timemachine]

Does any know how to open the ingnition cylinder on a 1984 GMC c3500 so that I can rearrange the wafers to re-code my lock with a good used one I have? I know I can buy a repop online that is inexpensive however, I would still like to know.

I have looked all over the internet for instructions and even my locksmith has no clue how to get it open. He also told me that GM has many different key configurations so not all keys will slide into a given cylinder.

Thanks for any help.