The Davis system will run on a stock GM module, but the module included with it is much better than an OE GM unit (hence my comment about an MSD module earlier). Part of the reason the GM HEI sucks is because of the dwell arrangement. As mentioned, having run the HEI in the past, in stock form it falls on its face at about 4,500RPM in OE form. Once GM got into the 7-pin, small-cap HEI it was a better setup because they let a computer control the spark's timing and dwell and they used a much higher-capacity coil that was no longer mounted in the cap. Of course, that first appeared on V8s with Tuned Port Injection, which fell on its face at 5,000RPM anyhow due to the crappy intake design. No amount of spark trickery could help that, which is why there were so many aftermarket TPI manifolds available way back when.
Believe it or don't, the GM HEI was modeled after Chrysler's setup. It's the same basic circuit, right down to the VR pickup. GM's failure to use a ballast resistor is one reason the HEI system was a high-RPM loser; the lack of a big, hardy transistor was another. The circuitry available at the time simply didn't allow for the enormous dwell times the Chrysler setup could deliver. It didn't matter at the time, since GM didn't have any free-revving engines available by the time HEI was introduced anyhow. Conversely, the Mopar system debuted exclusively on the high-revving 426 Hemi and screaming 340 in '71. They were the only two engines to get it that first year, and in '72 it was standard only on high-performance engines and Imperials. It wasn't standardized until '73.
