You could look into the IBM Selectric - the typing element is a ball so it can't jam, and it's actuated by little cables that might be hackable. Feed it paper off of a roll, and you have your jam-free, continuous printing solution :)
A few years ago I took apart my Correcting Selectric III with exactly this aim. IIRC there are around six levers which can be actuated in different combinations to select and imprint all of the symbols on the type ball. I had a lot of fun selecting them by hand to try to map all of the combinations.
IBM must have had this use in mind because they actually made a variation of the Selectric design that could be used as a serial terminal. We have one in storage at work but I think the mechanism is seized. Wikipedia has a surprisingly long section about modifying the Selectric to work as a computer terminal[1].
