You will need to isolate the output lines of the printers from each other. Ya don't directly tie two outputs togeather without going through a logic gate unless you want to fry some logic.
Does the printer have an ability to read status information back from it, and if so, are you wanting to do this?

If not, common the data bus lines up between the two printers. Use a transmission gate/multiple input latch (ala LS573) in a non latch mode to switch the various outputs from the printers to the microprocessor. Use one pin from the micro (i.e. the printer select pin) to select the printer and also the correct latch. You could even when selecting the latch use one of the input/output lines of the latch to select the printer if spare. Put an invertor on the printer select pin for one latch only such that a low on the pin selects one latch and a high selects the other.

From the data I have here, the Select In is the correct pin - I don't know if all printers adhere to this pin though. You could also acheive the same result by controlling which printer gets the /STROBE signal to clock the data. This will work for all printers. This could be sent through the latch to the desired printer as selected by the printer select pin as described above.

Hope this helps.