The Ford Duraspark ignitions are very good systems.They do how ever need mechanical modifications to perform properly in high performance applications,on the street or strip.The adjustments they offer in un-modified form are usually not adequate for performance applications.If you are into the mechanics of the system you can modify it to meet your requirements,although this is time consuming but not expensive.I use the Ford Duraspark systems or parts of the Duraspark system in ALL my applications(drag race,street,old and new cars)and with the proper modifications they all work great!...Livermore Dave.
The duraspark distributors often have a massive amount of mechanical advance. For instance many of the duraspark distributors have a choice between 32 degrees of mechanical advance or 42 degrees of mechanical advance. The width of the advance slot is what determines this. The only way to change it is to reduce the slot. I used JB weld on mine to close up the slot, but if you have access to a welder, you can weld it and grind it down to the size you need. Or you could try and find this piece which is replaceable from another duraspark distributor that has a smaller gap. The old points distributor usually had a choice between 20 or 26 degrees of mechanical advance. The advance slots are marked with a number (ie 10, 13, 16, 21). If you double that number that is how much mechanical advance the slot will give you. This stuff is all located underneath the plate on your distributor.