...I'am going with a Bad Coil*, Intermittent Failure. And, if you are running a Holley Carb, check for incorrect 'Idle Screw' setting, and Make sure the 'Idle MIXTURE' Screws a NOT Screwed in TOO FAR!! They should be OUT from closed-off, a Minimum of 1-1/2 Turns or More. Sure! With the Accelerator Pump SHOT, it WILL 'Fire Right UP'! But it will NOT Idle, for a Holley Carb.
* Test this, borrow a known Good Coil and Try it out on the Road.
Good-Luck with It!
MJ