I have done it several times. Start with these materials:
-a later Marx motor with double reduction gears and thin flange wheels. You can find these in many later Mark locos, both steam and diesel, but mostly steam.
Just swap the cross bar from the old "fat wheel" motor to the new "thin flange" motor. It's really that easy. No need to fuss around with different brands of motors. If the motor in your M 10005 is the newer single axle drive, you may have to drill one hole in each side of the body.
Marx made almost all of their stuff to the same dimensional standards.
You can go even further and put a can motor into that new Marx motor frame. I write that one up some time.