1970 340 has the 1973 low compression pistons

I love statements like this, when half the factors that affect detonation are left out.

Which is why I err on the conservative side of recommendations. People inadvertently just leave things out of their thought process. "Where" initial timing will really need to be, elevation, never considering how hot the car will get in stop and go traffic and on and on and on.

I like your boost idea, even though I'm a N/A guy. With boost, there's zero additional heat down low or at idle. It's just a low compression engine then. They'll idle in traffic all day long. Even naturally aspirated though, a low compression engine can make plenty of power with the right combination and right tune. I'm just not going to make a recommendation for someone to end up on the ragged edge and end up having detonation problems. If they make that decision, it's gonna be all theirs. lol