gap for plugs - MSD box & dist.

There are designs, such as Hemi's, that benefit from 2-plugs/cyl due to emissions factors. I worked at Chevron Research for 18 years in the fuels and lubricants areas and never say meaningful data showing that plug type improved ignition materially. There was marginal data showing the plug indexing made a difference, but not enough to see in drag strip times in a stock 340.
Fuel combusts in milliseconds. The flame front travels from spark source across the cylinder and consumes fuel producing power. Multiple sparks may help a marginal design fire more reliably, but this does not increase power which is determined by the amount of fuel/air available and the ratio of each. Engines burn 99+% of available fuel or they would not meet emissions requirements and the cats/traps wouldn't work.
What does make power is proper Air/Fuel ratio and timing along with combustion chamber design and port flow (more air is better). Spark has no impact once the flame is initiated properly. Advanced plugs may be more reliable over time (Platinum, etc.), but cannot increase power as power is produced by fuel, not spark. So, if a new ignition system increases power, there was something deficient in the old system. Or it wasn't Fit For Purpose such as high compression ratio or high engine speed. Generally, Street Engines will not see a benefit for advanced ignition systems other than reliability.
And you still need vacuum advance under part-throttle conditions for maximum FE.