Ditto on the Duraspark II. Replaced my Load-o-matic dizzy (which was already running a Pertronix I unit) about two weeks ago. I also recurved the DSII according to the sticky at the top of the page. I picked up a solid 2 mpg (now 20 as opposed to 18 ) in around town driving (and some of the hottest weather so far this year... 95+ degrees).
My Holley 1940 carb doesn't have the SCV so I know that my old LOM dizzy was not getting the proper advance signal... ditching the LOM was probably the primary contributing factor to the MPG increase. But I must say that the car starts MUCH more easily now... and my idle has smoothed out considerably.
FWIW, I have my old plugs gapped at .045, and set initial timing at 6*. I'm running the DSII vacuum from the manifold. I don't trust the spark port on my 1940 carb (which is in bad need of a rebuild/replacement anyway).
After this next tank of gas, I'm going to advance the initial timing to 10* and see how it affects my mpg.
Before I get too far into the Fall, I'm going to replace the carb... likely with the Holley 5200 progressive 2 barrel.
Anyone want to buy my Pertronix I? It only has about 3,000 miles on it and works fine.