Hello
Sometimes the best way to make sure the valve lifter is on the base of the cam is set the intake valve when the exhaust valve is open and the exhaust when the intake is open.
Due each cylinder, crank the engine over until the intake valve is up and the exhaust is down (set the intake valve) then crank engine till the intake is down and the exhaust is up (set the exhaust valve.The feeler gauge should have a small amount of drag on it when sliding it between the valve and rocker arm.
If you have any wear in the valve train it would be in the rocker shaft and at the rocker arm tip that pushes on the top of the valve.
the way to set the timing is to disconnect the vacuum line and plug the port, using a timing light set the timing, the timing marks are on the flywheel, you can see them through the hole with the pointer at the front of the bell housing. Then reconnect the vacuum advance.
It sounds like your setting the timing were it sounds the best and then adding the advance which is over advancing the timing.
