First, you cannot use a volt meter to check the high voltage side...just like Corvette64 said.

Second, remove your cap and rotor. Look at the rotor closely on both sides near the center. HEI rotors typically fail by arcing thru the plastic near the center and allow a ground to the distributor shaft. The symptom begins as a random miss and eventually grounds the thing entirely. If it is a white rotor, the arc hole is easy to spot, on a black rotor, it is tougher to see.

mike in tucson