Right, as I said in the initial post, the timing would have to be retarded.
FWIW, it seems that some DRs used a single, two lead coil, and some used two, single lead coils.
I'll look for a good used DR ignition box and a single, two lead coil. And try to make it work with the Savage trigger.
No matter what coil I use, both will fire at the same time. Although there have been experiments with slightly different timing between two plugs on one head, I believe all of the mass produced systems fire both plugs at once.
The idea is that the flame travel distance is reduced. Part of what causes detonation is the pressure building up in a large, wide combustion chamber ahead of the flame front. By reducing the flame travel distance, the time required to burn the mixture is reduced, hence the reduced timing.
Honda did a lot of experiments in the early 60's as their 6 cylinder 250s revved to previously unheard of RPMs. At first they thought that timing would have to be advanced throughout the RPM range. What they found was that the increased turbulence of the faster incoming charge moved the flame front around faster, so there was a limit to the amount of timing needed. In those days, many motors used a steep included valve angle to allow large valves, owing to sub-optimal ports. Therefor, timing was quite advanced by modern standards because the flame had to travel over the hump of a high compression piston in a combustion chamber that looked like a TeePee.
When Cosworth in England come up with better ports and a flatter 4 valve combustion chamber, timing on those motors was in the high 20's. Even the twin-plug BMW Superbikes in the mid-80's used only 28-30 degrees of timing on their 2 valve heads.
It wasn't until Yamaha tried their 5 valve heads in Superbike, and ended up with a crazy wide, thin, flat combustion chamber that ignition timing headed toward the 40+degree territory to get the mixture at the peripheral areas to burn.
Part of what speeds up combustion is the turbulence in the head. I've made some mention of tightening the squish band. I've done this on other motors, and it makes a noticeable difference in power. The mixture in the perimeter of the combustion chamber is 'squished' in toward the center.
Because I have to start somewhere, I'll start with 1mm/.040".
Not sure anyone asked....
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