I'm not a tuggie, but characterising a strange motor is generally not too difficult
Are there any holes in the casing/end bells? No, probably not.
If there had been you would have been able to count the poles - basically the more the merrier for a tug
Sometimes turning the shaft by hand will allow you to feel the "cogging" as the poles pass the magnets - again the knobblier and more knobbles the better. (strong knobbles means small airgaps and strong magnets - both good for efficiency - frequent knobbles mean many poles - good for torque)
Hitch her up to some power - maybe 6V or a buggy pack. what speed do you get? can you stop the shaft using a calibrated FLJ?
Does it feel slow and torquey?
If you are feeling VERY scientific you could lash it all up to a plank with shaft and prop (take off the belt pulley first, if possible) immerse prop in bath, measure current, rpm and remaining water in bath after 10 seconds. Mop up bathroom
So if its a multi-pole motor, with loads of torque it would seem to be quite suitable. If it is said to be wound for 12 or 18V it is certainly wound with fine wire, and should have ample torque.
Good luck - keep us posted, please
The expert tug drivers will no doubt reply shortly