picture of inside of a Pertronix dist.

So per Pertronix this morning they say for the IBS-4013 distributor I should be using Pertronix 1584.

https://www.speedwaymotors.com/PerTronix-1584-Prestolite-Ignitor-8-Cylinder,300888.html
Summit says this is for an IBS-4012. Speedway has it on sale but says it may not fit. Anyone know the difference between and IBS-4012 and an IBS-4013? Anyone ever use this particular Pertronix conversion kit?

Thanks!