Did you check to make sure the harmonic balancer is still good? They tend to slip after a while on 292's and the timing marks end up being incorrect.
You may be seeing the vacuum advance coming in with your throttle blipping. Disconnect the line at the carb and plug the hole.
Too tight valves will cause the engine to lose compression when hot and can cause poor idle and hot running, due to the exhaust valves not spending enough time on the valve seats. It is best to run slightly to the loose side of spec on a stock engine, especially in the summer; it does not hurt anything and helps the valves run cooler.
I had let the lifter adjustments on my 6 cylinder BMW go for too long once and was getting an intermittant check engine light and a code for a bad lambda sensor, along with poor gas milage and rough idle. I knew the sensor was good, so I did a tuneup and valve adjustment and it fixed it. The valves were too tight.
