1969 dart loses spark once it warms up

Hwy guys hope someone can help I have a 69 dart with a 360 it has MSD ignition (6al box) with a msd blaster coil and the distributor has been converted to electronic from points. It will start up fine when it has been sitting once it warns up it will lose its spark and stall and not start till it cools down again any ideas?[/QUOT

So I was told at a MSD dealer to make sure my coil was mounted vertical .So I got a new coil mounted it and still the same. Started right away let it run for half an hour shut it off waited 15 min and would not start no spark from the plugs. I have spark from the coil . I think i will try changing the distributor tomorrow. That is all that is left .the MSd box and coil are new hope that solves the problem.