The engine manufacturers put a stop to the cam walk problem when they went too hydraulic roller cams. They incorperated a bolt on plate to the front of the block and pinched the cam with the timing gear. That stopped forward and rearward movement of the cam, but they also went to a crank trigger ign.
The main problem with cam walk other than timing fluation is it with put escessive wear on the distributor gear, even more so with a bronze gear. That's another thing you need to look at for your timing problem, the gear could have some wear.
Go to Google and type in camshaft walk, there's several good reads about cam walk about the reasons and the way different engine builders have addressed the problem.
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