I've got a '64 Wildcat with 109,000 miles on the clock with a stock 401 (internally) that has never been apart as far as I know. The engine runs very well and burns/leaks little oil, maybe 1 quart per every 1000 miles. The compression pressures average 155 psi with a warm compression test. The max was 165 psi and the min was 145 psi. Using a bore scope it appears it still has the OE timing chain and sprockets. I need to replace the OE timing chain and sprockets for insurance and have been kicking around the idea of dropping in a TA-20 or TA-25 cam, lifters, and stage 1 valve springs. I do not plan to remove the heads. The engine runs too good to consider a full rebuild (and the $$$ isn't available at this time). I'd like to pick up a little performance now instead of withing a few years until the $$$ is available for a performance rebuild, but am concerned that the extra fuel and air may cause sealing issues with the rings. It responded very well to a recent ignition recurve so I hope a new cam will pep it up even more. I plan to run the engine with a rebuilt ST-400 with switch pitch.