Just a quick heads-up for anyone considering trying a HEI with 6 volts- - - - - -nope, it doesn't work. I tried using a DC rectified variable-voltage power supply on the training HEI in my distributor tester, and at anything below about 9 volts, the spark just shuts off. When (if) I get hold of a well-charged 6 volt battery I'll try again, but it doesn't look too promising. At any voltage below about 10.5, the spark gets noticeably weaker. 15 volts makes it look like a lightning strike across the plug electrodes.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!