A 74LS243 is a bus tranceiver on a PRINTED CIRCUIT BOARD. It is not a cable driver, 18 inches is about the maximum run for an LSTTL output.
There are any number of simple solutions including the multi-drop RS-485 trnasceiver which can drive twisted pair or coax or any other transmission line you may have in mind.
You might also consider the quasi-differential with respect to a common ground transceiver used on DeviceNet. It is made by Philips, the 82C251, and it can drive 500 meters at 125 kBaud.
The discrete solution consists of something like a class AB push-pull stage that drives the cable both high and low. There are some other alternatives depending on your requirements and budget parameters.