I made one for my RM by welding together 4 bits of 50mm angle, with holes in each arm for stator cover bolts to go through, and a large hole in the middle through which to put an ordinary 2 or 3 leg puller, with the centre puller onto end of crank, and the legs hooked under the angle. You need to be fairly accurate with your holes, and make sure the whole thing sits square by adding washers to each bolt as necessary or using longer bolts with travelling nuts. An alternative method is to not use the puller at all, and just use the longer bolts with the travelling nuts, and go around them a half turn a time or so. Make sure to use the travelling nuts and that the bolts are right home. Of course, this tool is model specific, but if you wanted to be more creative you might want to try a similar thing but instead of welding together bits of angle get a circular flat steel plate at least 5mm thick, and drill your bolt holes as necessary.
