Yeah, spark curves...my 1967 Ford LTD 2-door fastback had a 2-bbl carb, but with a 2-stage distributor that reached 18 degrees at 2200 RPM and stayed there until about 2800 RPM-ish, then could reach 45 (!) degrees at 4800 RPM (and more than 120 MPH indicated). That car NEVER struggled, even in the highest mountain passes.
I've long wanted to figure out how to do this with an SOHC4 engine, and might get a shot at it next Spring. The 'first' spring in the Ford distributor was light and looked & acted normally, while the 'second' spring (opposite the first one) was stiffer and had an elongated loop on one end that reached zero clearance when the first spring was at 18 degrees, temporarily halting the advance angle at that point. This held until enough RPM started overcoming that 2nd heavier spring, and then both of them stretched out to reach the 45 degree mark. Clever setup, would like to try it on a 750...you could feel it in the Ford: the first advance gave it quickness in city traffic (30-ish MPH) and there was a small flat spot when jumping onto freeway onramps, then it just launched like a 4-bbl feels.