If you have the pickups and advancer-rotor, you can make an ignitor for about $30 or $40.
www.geocities.com/loudgpz/GPZgmHEImod.html
If you go that route, I may be altering the schematic a little. Sometimes if the battery is very weak, it won't get a spark during cold-cranking. I may change R1 to 500 ohms instead of 1000.