Some of the squirrel cages have a slotted screw holding the cage to the motor.Some have a push on clip on the tip of the motor shaft that hold the cage in place.If you don't see any signs of either one,the clip probably fell off or was removed by the previous owner.Put a little heat on the tip of the shaft"propane torch" and see if the cage will slide off.
Yes,when you get the blower cage off,there are two nuts holding the motor onto the sheet metal.
12 volt motors are easily installed.you will have to drill two new mounting holes.
That is a very nice air flow heater unit to start with.
Tim
1951 3100 Chevrolet1951 Chevrolet Suburban CarryallImage"A house is built with boards and beams. A home is built with love and dreams."
"Look deep before you leap !!!" / "Everything is Everything"
"If I say a mouse can pull a house, hitch him up"