I like the sound of a pony motor starter for a two cylinder John Deere tractor. The 720 diesel I am most familiar with had a little V-4 engine that would run at something like 6000 rpm. This engine had a clutch which when engaged turned over the main diesel engine. Once the diesel engine was spinning over, the diesel engine speed lever was moved forward, which allowed fuel to be injected into the engine, and it started. If it was really cold, the operator would start the pony motor and let it run for a while. The pony motor was water cooled and circulated warm water through the diesel block. Also, the exhaust from the pony motor went into the intake of the diesel engine, which warmed up the combustion chambers quicker, and allowed for quicker, cleaner starts. I know there are videos of this procedure on u-tube and if I could figure it out I would post them here.
Also look up starting a John Deere R. The process is similar, the pony motor on the R was a two cylinder instead of a V4.