Spark plugs are always a good place to start when a car won't run smoothly, I'm guessing you've tried that. Ignition parts are cheap. A new set of points, condensor and plugs usually takes care of it when my cars run rough. Check the distributor cap, are any of the terminals green/corroded? That happens a lot on cars that are not driven regularly.
What all have you tried? What tools do you have available? A dwell meter and timing light can do wonders on these old cars. Also, a compression tester is a good piece of equipment to have if a car runs rough. Run a compression test - all six cylinders should have relatively the same compression. If not, you could have a tappet that needs to be reset, or a burned valve which is fairly common in the KF 226 engine. Possibly a leaky head gasket, but a leaky head gasket would cause white smoke and visible leaks when the engine is warm. Modern fuel also causes problems with the accelerator pump diaphrams in the carburettor.