1968 340 timing

The statement that too much timing breaks motor parts, applies to WOT; Wide Open Throttle. The thing you have to listen for is DETONATION. This has to be avoided at ALL cost/ no matter what.
Your Power Timing at WOT, depending on your set up, will usually want to be at 34/36, after 3600rpm. Not every combo will accept 36 and not every combo will accept 36 before 3600. Only you or your tuner can figure it out. Nor do you have to push the limit from day one. It is better to be 3 or 4 degrees SHORT of optimum, than even just one degree too much. Your butt-dyno will not feel the difference of 2* short of optimum power timing.Maybe not even 3 or 4 degrees.
So the operative is to sneak up on the max PowerTiming over time. Lots of time.