The generic 7414 Schmidt Trigger chip is widely used for interfacing, but most of the variants have quite a low drive capacity, and some do not get close to the rails. The version you need is the 74ACT14: that chip is the bees knees for interfacing as it can drive up to 24 mA each way. It is a plug-in replacement for the the other versions.
Second thought: put all these 'interface' chips in good sockets. Servicing becomes so easy when you can flip a chip out and plug another in just like that. But CAUTION: when inserting an IC into holes or into a socket, make very sure that ALL the pins are going in. If a pin gets curled up under the chip it is impossible to see it, but the chip won't work as it should. I know ...