My old school 340 upgrades and results.

I would say by what I heard in the video, and what the symptoms are, it's electrical. I could very well be wrong. It's not fuel delivery, or it wouldn't do it until you are under load. You are running strong for short-shifting it. If it was a cam problem, it would show it's face by the performance it made. I say your electrical system is messed up, and I still say I would just do a MP electronic conversion kit. I've heard of some stories with MSD ignitions giving some problems (not hating on MSD at all). Just say'n.