[rotorwrench]

The 6-volt coil will work with the 12-volt systems just fine as long as you use a ballast resistor and 1.5 Ohms should do OK. That will cut the voltage back to the 6-volt level and keep the amperage under control. All the other charging system stuff in not needed except to add a fan for cooling and keep your water pumps turning if you are goind to use a radiator cooling system. The polarity has to be reversed on the old coil for negative earth and you need to veryfy that the old coil is still functional. The "Dist" connection would become the "Bat" connection if you reverse polarity. With 12-volts you would only need 18 guage wire for hook up. 16-guage would be overkill. Coils made for 12-volt systems usually have enough internal resistance that they don't need a ballast. One can be used though but the ballast resistance could be less than .5 Ohm to be effective.

Most folks agree that extended running of an engine (especially a fresh rebuild) is not a good idea unless you have the capability to load it with a water brake or by turning something else to apply load. You can start at idle for a bit & check for leaks but thats about it. An engine really has to be loaded in order to break it in properly. I just use wires with aligator clips on them for hook up & disconnect. You can turn the starter with jumper cables just to get it running. I use direct reading oil pressure & temp guages along with a infrared temp gun to check for hot spots. Anything more elamorate than that is a waist of valuable time in my opinion. Now if you have an old saw mill and need to cut some lumber then that's different.