I'm looking at a 1957 640 (don't pay any attention to the Workmaster 601 on the hood). The model number on the transmission housing states "640" and the serial number is 144234. And there is a trace of 640 on the left dogleg.
The owner says the ignition switch is bad (it's been replaced with a push/pull switch) as he had to wriggle it to start it when he first got it and now it won't start. The pto seal will have to be replaced and possibly the bearing (I can't tell if the looseness is in it or the overrun clutch). The steering box is probably leaking to as there is some oil buildup on it.
He wants a $1000 for it.