Remove a metal door frame

In a house I am just moving into, built in 1956, there are several interior doors with metal frames. I`d really like to replace these with pre-hung doors with wood frames. The frame is pretty stiff sheet metal. I took off the hinges and the strikeplate and I can see the wood of the rough opening inside, and that the frame is basially hollow -- there is space between the wood and the metal. Of course it is covered with many layers of paint and I can`t find and screws or fasteners and I can`t see how the damn thing is fastened in place. Around the edge, all the way around where it meets the plaster wall there is a shallow groove about 1/8" wide. I scraped away a bit of the paint there and could see that there doesn`t seem to be any edge to the metal, it is appraently folded under itself there. Any ideas on how to extricate this thing?
Thanks in advance!

For the most part bottom of the side jam away toward the center of the door. Namely this should allow it to disconnect from the top. For one the top may or may not be anonymously attached so subconsciously watch your head.