I'd like to thank you guys for the information you provided regarding timing and valve clearance on my 292. After many days of diagnosing the cause of burnt exhaust valves and loss of power under load, I'm finally satisfied with the results. I finally gave up on troubleshooting the ignition system and focused on the fuel system. I assumed that the vacumn test I performed on the fuel pump (14 in. of vacumn) was sufficient. However, as a last resort, I attached a clear fuel line between the existing fuel line and the fuel pump, and was greeted with air bubbles. After tracing it back, I discovered that the suction line within the fuel tank behind the seat must have developed a leak, which caused the engine to run lean and burn the valves. I hope someone may find this of interest, or may help someone else diagnose a similar problem.