Tom, the first thing to check is the trigger voltage. Some film era flashes used trigger voltages high enough to fry your digital camera. The source for this is:
Photo Strobe Trigger Voltages or you can check the voltage yourself if you have a digital multimeter. In general a trigger voltage of less than 12v is considered safe for Pentax.
The next question is "will it work" and the answer is usually "maybe". If you mean in full TTL mode with auto exposure, then most likely no. If you mean in full manual with the power controlled on the flash and the camera providing only a 'fire' command then most likely yes.
Pentax now uses it's own TTL signaling called P-TTL and there are only a few third party flashes that support that. Not sure exactly when they moved from TTL to P-TTL.