1. close the top of your mold so there is just a small neck.
2. cool it slower.
3. even in real life the open part of the mold is rough and irregular, further processing (grinding, milling) is required to clean up the rough spots. without closing the mold or cutting off the scrap, it is going to be rough.
well man I wish you the best of luck.
Couldnt it just be compiled at let it be released unofficial?