A standard mini-DIN-8 serial cable is indeed all that is needed. I have done it myself on numerous occasions. The trick there, and the reason it likely didn’t work for you, is that there are two different kinds of such cables. Most of them are wired such that the “transmit” pins at each end are connected to the “receive” pins at the other. That is the kind you need. Unfortunately, some early Apple printers had their ports wired with the transmit and receive pins the opposite way around from the ones on the back of the computer (probably because that was the way it always used to be done in the old days of serial terminals). Accordingly, cables for those printers will not work with newer printers, and in particular, will not work to connect two Macs directly.

The two kinds of cables are identical in outward appearance, and as far as I can tell there was never any standard way of naming them so a purchaser could be sure of what he was getting. The best that people have managed in the past was to name one kind of printer that the cable in question definitely worked with. I THINK (for goodness’ sake verify this before spending any money!) that a StyleWriter II cable will be of the correct type.