Keep in mind the path you will be cutting is helical. That will effect the geometry if you attempt to use a form cutter in a boring head/fly cutter, or similar setup, unless you are planning on using a rigid tap cycle to co-ordinate Z axis and spindle motion (similar to what you would do when threading on a lathe). If you are doing that, the form cutter would match the worm profile exactly, just make sure you have enough relief on the tool.