The simplest, most reliable conversion is the GM HEI system from a 230/250/292 engine, but it requires converting to 12 volts. The modification of the distributor housing has been covered repeatedly here, and I believe there's a tech tip on it. I don't think anyone has figured out how to do a simple electronic ignition conversion on a 6 volt system without going to an expensive, unreliable aftermarket setup with proprietary parts.
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!