Transmitting digital signal long distances, without complex parts
You could put a bipolar transistor in emitter follower configuration on each TTL output, to lower the output impedance and boost current capability. Otherwise, I would expect various telecomms line drivers to be available to suit your needs. Presumably you are using signal-return paired connections, as well as an overall 0V line and protective shield/ground.
If the environment is electromagnetically noisy then you might also want to use co-ax or shielded-pair cable to provide individual shielding as well as the line return paths; just make sure there is 100 ohms or so in series in any 0v or ground loop. Some more general EMI filtering might also be appropriate, depending on the nature of the environment.