There are some '51 derivatives which can have the ports be programmed as push-pull stages. These will show very low output impedances and are suited to drive longer lines.
Nevertheless, it's the rise time of signal which determines how long the line can be. If the rise time is very short and the lines very long, then you will suffer from transmission line effects. Means, you get trouble with reflections and echoes, unless you use proper termination of the lines. If you need the full bandwidth, then series termination is adequate. But if you don't need the full bandwidth, for instance because you only control some relays or similar, then a simple low pass filter in series to port output can be used. This will help to avoid reflections and to suppress radiation effects. Something in the range of 1...2.2k + 47pF is a good choice.

Kai