You dont have to cut with a saw. Build the master with the lip. Make your mold. Lube the surface of the lip slot in the mold, and pour some more silicone in the lip slot to fill it. When it cures, remove it. Now you can make a lipped bait, or load the silicone slug in and make a lipless.
This way your lip will always be straight. When you mold without the lip you may get a little flash but can easily clean that up.
Regards
Sonny