Electronic ignition upgrade.

From what I have read and experienced with my 340 for 54 years is that ignition timing and advance curve are paramount to a good running engine. Once the spark is stable at all RPM's the engine will see, the power is in the timing curve. The 340 seems to like 34° mechanical advance for best 1/4 mile MPH. From there, use the advance plate with the least advance or weld to shorten. I use an 11° advance plate (distributor advance degrees). This is 22° crank advance, so initial advance is 12° for a total of 34°. The rest is in the advance springs to eliminate any detonation. The quicker the advance, the more power to the point where advance is optimum for the combustion chamber design and cam.
I got my stock 340 to a 13.48 @ 105.38 with a 3300 lb '68 Formula S FB using this approach. Could have done a better ET with more tire and gear (3.55), but never went that way.