28* initial timing for a 318? How can that be?

"All in" is practically meaningless without an rpm. It's right up there with 3/4 race cam.
If that's at 2500 rpm, that's way too quick to use with vacuum advance.
The fast advance curve and no vacuum advance is from the days of points ignition and drag racing. Vacuum advance was just one more thing not needed for drag racing and eliminating it simplified things and could be used to lock the rotor phasing.

Higher or lower initial timing is also not helpful. Plot a specific timing curve and then we can talk. Will be here for hours discussing all the possibilities and then how to tune them. Sometimes things don't act like you think they will. Then you got to figure out why. Like the example Shrinker gave of making the air fuel ratio richer and getting a cleaner burn.

As far as your guesses on torque and hp peaks, they are a bit low. There's some dyno pulls posted for stock and modified 340s. You can search them out. Some from Hot Rod magazine 1969 in this thread
https://www.forabodiesonly.com/mopar/threads/lets-revisit-timing.499590/