my original query was as to some sort of rule of thumb for motor power (meaning torque of course) to vehicle all up weight which will allow single speed transmission.
I'm very sorry, you can't have one.
Cedric can give you an estimate for his motor because he knows all the performance curves, but your whole approach seems to be based around finding a surplus motor and trying to determine if it might do the job.
With motor torque rarely being quoted in specifications but knowing that total output in kw is in fact a function of torque and rpm it did not seem unreasonable to me to ask for a rough ratio of kw to kgs to permit the use of a nice simple single speed conversion
Unfortunately it IS unreasonable, there are just too many factors to take into account. Two motors with the same Kw ratings can have such wildly different characteristics that one will do the job just fine, whilst the other will burn out almost immediately. Maximum safe rpm, maximum safe voltage, the ability to handle overload currents, cooling, thermal mass, etc. are all factors that will affect the suitability of a motor for a particular application.
If you go through the archives of the Electric Vehicle Discussion email list you will find countless stories of burnt out motors, controllers and failed batteries. Many of these failures will have been becuase someone followed a 'rule of thumb' without understanding why that rule did not apply in their particular case.
Let me ask you, 'how many horsepower (Internal combustion engine) do I need for a 1000Kg vehicle?'