We have installed many, many Wood cams and we have also done long term testing specifically on the effects on the valvetrain. There is no more stress on the valvetrain with the TW6-6 or TW-555 cams than with other similar performance cams, if there was any question running them in a 96" we would note specific requirements to do so. The TW-555 is really just a variation of the TW6-6 with .0045 more lift and 2 more degrees of duration. Most interesting is that your tuner was recommending the Mackie 575 cam which has more lift than the TW-555, and with .575 lift the Mackie 575's are near the threshold of what is considered safe with stock valve springs.