Ignition problem I think?

Hi I have a 1970 Dodge Swinger with a 318 & new Holley 650. This is a strange problem I'm haveing here and I hope one of you can help me with it. After the car has warmed up It will stall. It will only do this when I'm idleing at a light or when I'm comeing to a stop but it only seems to do it once. It has never done it while accelerating of while driveing. it will not start again for about 30 to 40 seconds then it seems fine. Then the next day it will do it again and so on through the week. I dont have time to check for spark because the problem will fix itself before i can check it Wierd hu. I have a new MSD Box & coil. I tested the ignition wire that turns on the box as soon as this happens to see if maybe it was turning the box off and it's fine. I don't think it's fuel because when it stalled in my driveway I check the carb for fuel flow and it sprayed fuel. It's not bogging out it shuts off like I've turned off the key. i thought maybe a bad coil tryed another one same thing. I noticed that one of my spark plug wires is sliced down to the center of the wire close to the headers can spark be jumping over to the headers and shorting something out? The distributor is the only part that's not brand new for ignition system. Could the distributor be causeing this? This problem began with my old electronic ignition that's why i put in the MSD. All the elictric seems fine when this happens all lights work car cranks over fine and when the car runs it runs very strong & beautifuly. Any idea thank you. JIM 8)